diff --git a/.eslintrc.js b/.eslintrc.cjs
similarity index 88%
rename from .eslintrc.js
rename to .eslintrc.cjs
index ce75c5c..a139e2b 100644
--- a/.eslintrc.js
+++ b/.eslintrc.cjs
@@ -5,7 +5,8 @@ module.exports = {
         "mocha": true
     },
     "parserOptions": {
-        "ecmaVersion": 2017
+        "ecmaVersion": 2022,
+        "sourceType": "module"
     },
     "extends": "eslint:recommended",
     "rules": {
diff --git a/build/main.cjs b/build/main.cjs
index 1697598..948162a 100644
--- a/build/main.cjs
+++ b/build/main.cjs
@@ -23,13 +23,13 @@ limitations under the License.
 */
 
 function flatArray(a) {
-    var res = [];
+    let res = [];
     fillArray(res, a);
     return res;
 
     function fillArray(res, a) {
         if (Array.isArray(a)) {
-            for (let i=0; i<a.length; i++) {
+            for (let i = 0; i < a.length; i++) {
                 fillArray(res, a[i]);
             }
         } else {
@@ -42,38 +42,38 @@ function flatArray(a) {
 function normalize(n, prime) {
     let res = BigInt(n) % prime;
     if (res < 0) res += prime;
-    return res
+    return res;
 }
 
 function fnvHash(str) {
     const uint64_max = BigInt(2) ** BigInt(64);
     let hash = BigInt("0xCBF29CE484222325");
-    for (var i = 0; i < str.length; i++) {
-    hash ^= BigInt(str[i].charCodeAt());
-    hash *= BigInt(0x100000001B3);
-    hash %= uint64_max;
+    for (let i = 0; i < str.length; i++) {
+        hash ^= BigInt(str[i].charCodeAt(0));
+        hash *= BigInt(0x100000001B3);
+        hash %= uint64_max;
     }
     let shash = hash.toString(16);
     let n = 16 - shash.length;
-    shash = '0'.repeat(n).concat(shash);
+    shash = "0".repeat(n).concat(shash);
     return shash;
 }
 
 // Note that this pads zeros
-function toArray32(s,size) {
+function toArray32(s, size) {
     const res = []; //new Uint32Array(size); //has no unshift
     let rem = BigInt(s);
     const radix = BigInt(0x100000000);
     while (rem) {
-        res.unshift( Number(rem % radix));
+        res.unshift(Number(rem % radix));
         rem = rem / radix;
     }
     if (size) {
-    var i = size - res.length;
-    while (i>0) {
-        res.unshift(0);
-        i--;
-    }
+        let i = size - res.length;
+        while (i > 0) {
+            res.unshift(0);
+            i--;
+        }
     }
     return res;
 }
@@ -84,7 +84,6 @@ async function builder(code, options) {
     let instance;
     let wc;
     let memory;
-
     options = options || {};
 
     // Only circom 2 implements version lookup through exports in the WASM
@@ -93,27 +92,37 @@ async function builder(code, options) {
     let majorVersion = 1;
     // After Circom 2.0.7, Blaine added exported functions for getting minor and patch versions
     let minorVersion = 0;
-    // If we can't lookup the patch version, assume the lowest
+    // If we can't look up the patch version, assume the lowest
     let patchVersion = 0;
 
     let codeIsWebAssemblyInstance = false;
 
+    // If code is already prepared WebAssembly.Instance, we use it directly
     if (code instanceof WebAssembly.Instance) {
         instance = code;
         codeIsWebAssemblyInstance = true;
     } else {
         let memorySize = 32767;
+
+        if (options.memorySize) {
+            // make sure we have int
+            memorySize = parseInt(options.memorySize);
+            if (memorySize < 0) {
+                throw new Error("Invalid memory size");
+            }
+        }
+
         let memoryAllocated = false;
-        while (!memoryAllocated){
-            try{
-                memory = new WebAssembly.Memory({initial:memorySize});
+        while (!memoryAllocated) {
+            try {
+                memory = new WebAssembly.Memory({initial: memorySize});
                 memoryAllocated = true;
-            } catch(err){
-                if(memorySize === 1){
+            } catch (err) {
+                if (memorySize <= 1) {
                     throw err;
                 }
                 console.warn("Could not allocate " + memorySize * 1024 * 64 + " bytes. This may cause severe instability. Trying with " + memorySize * 1024 * 64 / 2 + " bytes");
-                memorySize = Math.floor(memorySize/2);
+                memorySize = Math.floor(memorySize / 2);
             }
         }
 
@@ -127,19 +136,19 @@ async function builder(code, options) {
                 "memory": memory
             },
             runtime: {
-                exceptionHandler: function(code) {
+                exceptionHandler: function (code) {
                     let err;
-                    if (code == 1) {
+                    if (code === 1) {
                         err = "Signal not found. ";
-                    } else if (code == 2) {
+                    } else if (code === 2) {
                         err = "Too many signals set. ";
-                    } else if (code == 3) {
+                    } else if (code === 3) {
                         err = "Signal already set. ";
-                    } else if (code == 4) {
+                    } else if (code === 4) {
                         err = "Assert Failed. ";
-                    } else if (code == 5) {
+                    } else if (code === 5) {
                         err = "Not enough memory. ";
-                    } else if (code == 6) {
+                    } else if (code === 6) {
                         err = "Input signal array access exceeds the size. ";
                     } else {
                         err = "Unknown error. ";
@@ -149,10 +158,10 @@ async function builder(code, options) {
                 },
                 // A new way of logging messages was added in Circom 2.0.7 that requires 2 new imports
                 // `printErrorMessage` and `writeBufferMessage`.
-                printErrorMessage: function() {
+                printErrorMessage: function () {
                     errStr += getMessage() + "\n";
                 },
-                writeBufferMessage: function() {
+                writeBufferMessage: function () {
                     const msg = getMessage();
                     // Any calls to `log()` will always end with a `\n`, so that's when we print and reset
                     if (msg === "\n") {
@@ -167,11 +176,11 @@ async function builder(code, options) {
                         msgStr += msg;
                     }
                 },
-                showSharedRWMemory: function() {
+                showSharedRWMemory: function () {
                     const shared_rw_memory_size = instance.exports.getFieldNumLen32();
                     const arr = new Uint32Array(shared_rw_memory_size);
-                    for (let j=0; j<shared_rw_memory_size; j++) {
-                        arr[shared_rw_memory_size-1-j] = instance.exports.readSharedRWMemory(j);
+                    for (let j = 0; j < shared_rw_memory_size; j++) {
+                        arr[shared_rw_memory_size - 1 - j] = instance.exports.readSharedRWMemory(j);
                     }
 
                     // In circom 2.0.7, they changed the log() function to allow strings and changed the
@@ -188,39 +197,39 @@ async function builder(code, options) {
                         console.log(ffjavascript.Scalar.fromArray(arr, 0x100000000));
                     }
                 },
-                error: function(code, pstr, a,b,c,d) {
+                error: function (code, pstr, a, b, c, d) {
                     let errStr;
-                    if (code == 7) {
-                        errStr=p2str(pstr) + " " + wc.getFr(b).toString() + " != " + wc.getFr(c).toString() + " " +p2str(d);
-                    } else if (code == 9) {
-                        errStr=p2str(pstr) + " " + wc.getFr(b).toString() + " " +p2str(c);
-                    } else if ((code == 5)&&(options.sym)) {
-                        errStr=p2str(pstr)+ " " + options.sym.labelIdx2Name[c];
+                    if (code === 7) {
+                        errStr = p2str(pstr) + " " + wc.getFr(b).toString() + " != " + wc.getFr(c).toString() + " " + p2str(d);
+                    } else if (code === 9) {
+                        errStr = p2str(pstr) + " " + wc.getFr(b).toString() + " " + p2str(c);
+                    } else if ((code === 5) && (options.sym)) {
+                        errStr = p2str(pstr) + " " + options.sym.labelIdx2Name[c];
                     } else {
-                        errStr=p2str(pstr)+ " " + a + " " + b + " " + c + " " + d;
+                        errStr = p2str(pstr) + " " + a + " " + b + " " + c + " " + d;
                     }
                     console.log("ERROR: ", code, errStr);
                     throw new Error(errStr);
                 },
-                log: function(a) {
+                log: function (a) {
                     console.log(wc.getFr(a).toString());
                 },
-                logGetSignal: function(signal, pVal) {
+                logGetSignal: function (signal, pVal) {
                     if (options.logGetSignal) {
-                        options.logGetSignal(signal, wc.getFr(pVal) );
+                        options.logGetSignal(signal, wc.getFr(pVal));
                     }
                 },
-                logSetSignal: function(signal, pVal) {
+                logSetSignal: function (signal, pVal) {
                     if (options.logSetSignal) {
-                        options.logSetSignal(signal, wc.getFr(pVal) );
+                        options.logSetSignal(signal, wc.getFr(pVal));
                     }
                 },
-                logStartComponent: function(cIdx) {
+                logStartComponent: function (cIdx) {
                     if (options.logStartComponent) {
                         options.logStartComponent(cIdx);
                     }
                 },
-                logFinishComponent: function(cIdx) {
+                logFinishComponent: function (cIdx) {
                     if (options.logFinishComponent) {
                         options.logFinishComponent(cIdx);
                     }
@@ -229,13 +238,13 @@ async function builder(code, options) {
         });
     }
 
-    if (typeof instance.exports.getVersion == 'function') {
+    if (typeof instance.exports.getVersion == "function") {
         majorVersion = instance.exports.getVersion();
     }
-    if (typeof instance.exports.getMinorVersion == 'function') {
+    if (typeof instance.exports.getMinorVersion == "function") {
         minorVersion = instance.exports.getMinorVersion();
     }
-    if (typeof instance.exports.getPatchVersion == 'function') {
+    if (typeof instance.exports.getPatchVersion == "function") {
         patchVersion = instance.exports.getPatchVersion();
     }
 
@@ -263,9 +272,9 @@ async function builder(code, options) {
     return wc;
 
     function getMessage() {
-        var message = "";
-        var c = instance.exports.getMessageChar();
-        while ( c != 0 ) {
+        let message = "";
+        let c = instance.exports.getMessageChar();
+        while (c !== 0) {
             message += String.fromCharCode(c);
             c = instance.exports.getMessageChar();
         }
@@ -277,11 +286,12 @@ async function builder(code, options) {
 
         const bytes = [];
 
-        for (let i=0; i8[p+i]>0; i++)  bytes.push(i8[p+i]);
+        for (let i = 0; i8[p + i] > 0; i++) bytes.push(i8[p + i]);
 
         return String.fromCharCode.apply(null, bytes);
     }
 }
+
 class WitnessCalculatorCircom1 {
     constructor(memory, instance, sanityCheck) {
         this.memory = memory;
@@ -292,8 +302,8 @@ class WitnessCalculatorCircom1 {
         const pRawPrime = this.instance.exports.getPRawPrime();
 
         const arr = new Array(this.n32);
-        for (let i=0; i<this.n32; i++) {
-            arr[this.n32-1-i] = this.i32[(pRawPrime >> 2) + i];
+        for (let i = 0; i < this.n32; i++) {
+            arr[this.n32 - 1 - i] = this.i32[(pRawPrime >> 2) + i];
         }
 
         this.prime = ffjavascript.Scalar.fromArray(arr, 0x100000000);
@@ -302,8 +312,8 @@ class WitnessCalculatorCircom1 {
 
         this.mask32 = ffjavascript.Scalar.fromString("FFFFFFFF", 16);
         this.NVars = this.instance.exports.getNVars();
-        this.n64 = Math.floor((this.Fr.bitLength - 1) / 64)+1;
-        this.R = this.Fr.e( ffjavascript.Scalar.shiftLeft(1 , this.n64*64));
+        this.n64 = Math.floor((this.Fr.bitLength - 1) / 64) + 1;
+        this.R = this.Fr.e(ffjavascript.Scalar.shiftLeft(1, this.n64 * 64));
         this.RInv = this.Fr.inv(this.R);
         this.sanityCheck = sanityCheck;
     }
@@ -317,10 +327,10 @@ class WitnessCalculatorCircom1 {
         const pSigOffset = this.allocInt();
         const pFr = this.allocFr();
         const keys = Object.keys(input);
-        keys.forEach( (k) => {
+        keys.forEach((k) => {
             const h = fnvHash(k);
-            const hMSB = parseInt(h.slice(0,8), 16);
-            const hLSB = parseInt(h.slice(8,16), 16);
+            const hMSB = parseInt(h.slice(0, 8), 16);
+            const hLSB = parseInt(h.slice(8, 16), 16);
             try {
                 this.instance.exports.getSignalOffset32(pSigOffset, 0, hMSB, hLSB);
             } catch (err) {
@@ -328,7 +338,7 @@ class WitnessCalculatorCircom1 {
             }
             const sigOffset = this.getInt(pSigOffset);
             const fArr = flatArray(input[k]);
-            for (let i=0; i<fArr.length; i++) {
+            for (let i = 0; i < fArr.length; i++) {
                 this.setFr(pFr, fArr[i]);
                 this.instance.exports.setSignal(0, 0, sigOffset + i, pFr);
             }
@@ -343,7 +353,7 @@ class WitnessCalculatorCircom1 {
 
         await self._doCalculateWitness(input, sanityCheck);
 
-        for (let i=0; i<self.NVars; i++) {
+        for (let i = 0; i < self.NVars; i++) {
             const pWitness = self.instance.exports.getPWitness(i);
             w.push(self.getFr(pWitness));
         }
@@ -369,32 +379,32 @@ class WitnessCalculatorCircom1 {
 
     allocInt() {
         const p = this.i32[0];
-        this.i32[0] = p+8;
+        this.i32[0] = p + 8;
         return p;
     }
 
     allocFr() {
         const p = this.i32[0];
-        this.i32[0] = p+this.n32*4 + 8;
+        this.i32[0] = p + this.n32 * 4 + 8;
         return p;
     }
 
     getInt(p) {
-        return this.i32[p>>2];
+        return this.i32[p >> 2];
     }
 
     setInt(p, v) {
-        this.i32[p>>2] = v;
+        this.i32[p >> 2] = v;
     }
 
     getFr(p) {
         const self = this;
-        const idx = (p>>2);
+        const idx = (p >> 2);
 
         if (self.i32[idx + 1] & 0x80000000) {
             const arr = new Array(self.n32);
-            for (let i=0; i<self.n32; i++) {
-                arr[self.n32-1-i] = self.i32[idx+2+i];
+            for (let i = 0; i < self.n32; i++) {
+                arr[self.n32 - 1 - i] = self.i32[idx + 2 + i];
             }
             const res = self.Fr.e(ffjavascript.Scalar.fromArray(arr, 0x100000000));
             if (self.i32[idx + 1] & 0x40000000) {
@@ -405,7 +415,7 @@ class WitnessCalculatorCircom1 {
 
         } else {
             if (self.i32[idx] & 0x80000000) {
-                return self.Fr.e( self.i32[idx] - 0x100000000);
+                return self.Fr.e(self.i32[idx] - 0x100000000);
             } else {
                 return self.Fr.e(self.i32[idx]);
             }
@@ -426,14 +436,13 @@ class WitnessCalculatorCircom1 {
         const minShort = self.Fr.neg(self.Fr.e("80000000", 16));
         const maxShort = self.Fr.e("7FFFFFFF", 16);
 
-        if (  (self.Fr.geq(v, minShort))
-            &&(self.Fr.leq(v, maxShort)))
-        {
+        if ((self.Fr.geq(v, minShort))
+            && (self.Fr.leq(v, maxShort))) {
             let a;
             if (self.Fr.geq(v, self.Fr.zero)) {
                 a = ffjavascript.Scalar.toNumber(v);
             } else {
-                a = ffjavascript.Scalar.toNumber( self.Fr.sub(v, minShort));
+                a = ffjavascript.Scalar.toNumber(self.Fr.sub(v, minShort));
                 a = a - 0x80000000;
                 a = 0x100000000 + a;
             }
@@ -445,10 +454,10 @@ class WitnessCalculatorCircom1 {
         self.i32[(p >> 2)] = 0;
         self.i32[(p >> 2) + 1] = 0x80000000;
         const arr = ffjavascript.Scalar.toArray(v, 0x100000000);
-        for (let i=0; i<self.n32; i++) {
-            const idx = arr.length-1-i;
+        for (let i = 0; i < self.n32; i++) {
+            const idx = arr.length - 1 - i;
 
-            if ( idx >=0) {
+            if (idx >= 0) {
                 self.i32[(p >> 2) + 2 + i] = arr[idx];
             } else {
                 self.i32[(p >> 2) + 2 + i] = 0;
@@ -466,8 +475,8 @@ class WitnessCalculatorCircom2 {
 
         this.instance.exports.getRawPrime();
         const arr = new Uint32Array(this.n32);
-        for (let i=0; i<this.n32; i++) {
-            arr[this.n32-1-i] = this.instance.exports.readSharedRWMemory(i);
+        for (let i = 0; i < this.n32; i++) {
+            arr[this.n32 - 1 - i] = this.instance.exports.readSharedRWMemory(i);
         }
         this.prime = ffjavascript.Scalar.fromArray(arr, 0x100000000);
 
@@ -484,17 +493,17 @@ class WitnessCalculatorCircom2 {
         //input is assumed to be a map from signals to arrays of bigints
         this.instance.exports.init((this.sanityCheck || sanityCheck) ? 1 : 0);
         const keys = Object.keys(input);
-        var input_counter = 0;
-        keys.forEach( (k) => {
+        let input_counter = 0;
+        keys.forEach((k) => {
             const h = fnvHash(k);
-            const hMSB = parseInt(h.slice(0,8), 16);
-            const hLSB = parseInt(h.slice(8,16), 16);
+            const hMSB = parseInt(h.slice(0, 8), 16);
+            const hLSB = parseInt(h.slice(8, 16), 16);
             const fArr = flatArray(input[k]);
             // Slight deviation from https://github.com/iden3/circom/blob/v2.1.6/code_producers/src/wasm_elements/common/witness_calculator.js
             // because I don't know when this exported function was added
-            if (typeof this.instance.exports.getInputSignalSize === 'function') {
+            if (typeof this.instance.exports.getInputSignalSize === "function") {
                 let signalSize = this.instance.exports.getInputSignalSize(hMSB, hLSB);
-                if (signalSize < 0){
+                if (signalSize < 0) {
                     throw new Error(`Signal ${k} not found\n`);
                 }
                 if (fArr.length < signalSize) {
@@ -504,13 +513,13 @@ class WitnessCalculatorCircom2 {
                     throw new Error(`Too many values for input signal ${k}\n`);
                 }
             }
-            for (let i=0; i<fArr.length; i++) {
-                const arrFr = toArray32(normalize(fArr[i],this.prime),this.n32);
-                for (let j=0; j<this.n32; j++) {
-                    this.instance.exports.writeSharedRWMemory(j,arrFr[this.n32-1-j]);
+            for (let i = 0; i < fArr.length; i++) {
+                const arrFr = toArray32(normalize(fArr[i], this.prime), this.n32);
+                for (let j = 0; j < this.n32; j++) {
+                    this.instance.exports.writeSharedRWMemory(j, arrFr[this.n32 - 1 - j]);
                 }
                 try {
-                    this.instance.exports.setInputSignal(hMSB, hLSB,i);
+                    this.instance.exports.setInputSignal(hMSB, hLSB, i);
                     input_counter++;
                 } catch (err) {
                     // console.log(`After adding signal ${i} of ${k}`)
@@ -529,11 +538,11 @@ class WitnessCalculatorCircom2 {
 
         await this._doCalculateWitness(input, sanityCheck);
 
-        for (let i=0; i<this.witnessSize; i++) {
+        for (let i = 0; i < this.witnessSize; i++) {
             this.instance.exports.getWitness(i);
-        const arr = new Uint32Array(this.n32);
-            for (let j=0; j<this.n32; j++) {
-            arr[this.n32-1-j] = this.instance.exports.readSharedRWMemory(j);
+            const arr = new Uint32Array(this.n32);
+            for (let j = 0; j < this.n32; j++) {
+                arr[this.n32 - 1 - j] = this.instance.exports.readSharedRWMemory(j);
             }
             w.push(ffjavascript.Scalar.fromArray(arr, 0x100000000));
         }
@@ -542,8 +551,8 @@ class WitnessCalculatorCircom2 {
     }
 
     async calculateWTNSBin(input, sanityCheck) {
-        const buff32 = new Uint32Array(this.witnessSize*this.n32+this.n32+11);
-        const buff = new  Uint8Array( buff32.buffer);
+        const buff32 = new Uint32Array(this.witnessSize * this.n32 + this.n32 + 11);
+        const buff = new Uint8Array(buff32.buffer);
         await this._doCalculateWitness(input, sanityCheck);
 
         //"wtns"
@@ -561,12 +570,12 @@ class WitnessCalculatorCircom2 {
         //id section 1
         buff32[3] = 1;
 
-        const n8 = this.n32*4;
+        const n8 = this.n32 * 4;
         //id section 1 length in 64bytes
         const idSection1length = 8 + n8;
         const idSection1lengthHex = idSection1length.toString(16);
-            buff32[4] = parseInt(idSection1lengthHex.slice(0,8), 16);
-            buff32[5] = parseInt(idSection1lengthHex.slice(8,16), 16);
+        buff32[4] = parseInt(idSection1lengthHex.slice(0, 8), 16);
+        buff32[5] = parseInt(idSection1lengthHex.slice(8, 16), 16);
 
         //this.n32
         buff32[6] = n8;
@@ -574,9 +583,9 @@ class WitnessCalculatorCircom2 {
         //prime number
         this.instance.exports.getRawPrime();
 
-        var pos = 7;
-        for (let j=0; j<this.n32; j++) {
-            buff32[pos+j] = this.instance.exports.readSharedRWMemory(j);
+        let pos = 7;
+        for (let j = 0; j < this.n32; j++) {
+            buff32[pos + j] = this.instance.exports.readSharedRWMemory(j);
         }
         pos += this.n32;
 
@@ -589,16 +598,16 @@ class WitnessCalculatorCircom2 {
         pos++;
 
         // section 2 length
-        const idSection2length = n8*this.witnessSize;
+        const idSection2length = n8 * this.witnessSize;
         const idSection2lengthHex = idSection2length.toString(16);
-        buff32[pos] = parseInt(idSection2lengthHex.slice(0,8), 16);
-        buff32[pos+1] = parseInt(idSection2lengthHex.slice(8,16), 16);
+        buff32[pos] = parseInt(idSection2lengthHex.slice(0, 8), 16);
+        buff32[pos + 1] = parseInt(idSection2lengthHex.slice(8, 16), 16);
 
         pos += 2;
-        for (let i=0; i<this.witnessSize; i++) {
+        for (let i = 0; i < this.witnessSize; i++) {
             this.instance.exports.getWitness(i);
-            for (let j=0; j<this.n32; j++) {
-                buff32[pos+j] = this.instance.exports.readSharedRWMemory(j);
+            for (let j = 0; j < this.n32; j++) {
+                buff32[pos + j] = this.instance.exports.readSharedRWMemory(j);
             }
             pos += this.n32;
         }
diff --git a/js/utils.js b/js/utils.js
index a11fe24..101862e 100644
--- a/js/utils.js
+++ b/js/utils.js
@@ -17,13 +17,13 @@ limitations under the License.
 */
 
 export function flatArray(a) {
-    var res = [];
+    let res = [];
     fillArray(res, a);
     return res;
 
     function fillArray(res, a) {
         if (Array.isArray(a)) {
-            for (let i=0; i<a.length; i++) {
+            for (let i = 0; i < a.length; i++) {
                 fillArray(res, a[i]);
             }
         } else {
@@ -34,40 +34,40 @@ export function flatArray(a) {
 
 // Ref https://github.com/iden3/circom/commit/ec6388cf6eb62463539cb4c40cc3ceae9826de19
 export function normalize(n, prime) {
-    let res = BigInt(n) % prime
-    if (res < 0) res += prime
-    return res
+    let res = BigInt(n) % prime;
+    if (res < 0) res += prime;
+    return res;
 }
 
 export function fnvHash(str) {
     const uint64_max = BigInt(2) ** BigInt(64);
     let hash = BigInt("0xCBF29CE484222325");
-    for (var i = 0; i < str.length; i++) {
-    hash ^= BigInt(str[i].charCodeAt());
-    hash *= BigInt(0x100000001B3);
-    hash %= uint64_max;
+    for (let i = 0; i < str.length; i++) {
+        hash ^= BigInt(str[i].charCodeAt(0));
+        hash *= BigInt(0x100000001B3);
+        hash %= uint64_max;
     }
     let shash = hash.toString(16);
     let n = 16 - shash.length;
-    shash = '0'.repeat(n).concat(shash);
+    shash = "0".repeat(n).concat(shash);
     return shash;
 }
 
 // Note that this pads zeros
-export function toArray32(s,size) {
+export function toArray32(s, size) {
     const res = []; //new Uint32Array(size); //has no unshift
     let rem = BigInt(s);
     const radix = BigInt(0x100000000);
     while (rem) {
-        res.unshift( Number(rem % radix));
+        res.unshift(Number(rem % radix));
         rem = rem / radix;
     }
     if (size) {
-    var i = size - res.length;
-    while (i>0) {
-        res.unshift(0);
-        i--;
-    }
+        let i = size - res.length;
+        while (i > 0) {
+            res.unshift(0);
+            i--;
+        }
     }
     return res;
 }
diff --git a/js/witness_calculator.js b/js/witness_calculator.js
index ca96f27..c2522d8 100644
--- a/js/witness_calculator.js
+++ b/js/witness_calculator.js
@@ -17,14 +17,13 @@ limitations under the License.
 
 */
 
-import { flatArray, fnvHash, toArray32, normalize } from "./utils.js";
-import { Scalar, F1Field } from "ffjavascript";
+import {flatArray, fnvHash, toArray32, normalize} from "./utils.js";
+import {Scalar, F1Field} from "ffjavascript";
 
 export default async function builder(code, options) {
     let instance;
     let wc;
     let memory;
-
     options = options || {};
 
     // Only circom 2 implements version lookup through exports in the WASM
@@ -33,27 +32,37 @@ export default async function builder(code, options) {
     let majorVersion = 1;
     // After Circom 2.0.7, Blaine added exported functions for getting minor and patch versions
     let minorVersion = 0;
-    // If we can't lookup the patch version, assume the lowest
+    // If we can't look up the patch version, assume the lowest
     let patchVersion = 0;
 
     let codeIsWebAssemblyInstance = false;
 
+    // If code is already prepared WebAssembly.Instance, we use it directly
     if (code instanceof WebAssembly.Instance) {
         instance = code;
         codeIsWebAssemblyInstance = true;
     } else {
         let memorySize = 32767;
+
+        if (options.memorySize) {
+            // make sure we have int
+            memorySize = parseInt(options.memorySize);
+            if (memorySize < 0) {
+                throw new Error("Invalid memory size");
+            }
+        }
+
         let memoryAllocated = false;
-        while (!memoryAllocated){
-            try{
-                memory = new WebAssembly.Memory({initial:memorySize});
+        while (!memoryAllocated) {
+            try {
+                memory = new WebAssembly.Memory({initial: memorySize});
                 memoryAllocated = true;
-            } catch(err){
-                if(memorySize === 1){
+            } catch (err) {
+                if (memorySize <= 1) {
                     throw err;
                 }
                 console.warn("Could not allocate " + memorySize * 1024 * 64 + " bytes. This may cause severe instability. Trying with " + memorySize * 1024 * 64 / 2 + " bytes");
-                memorySize = Math.floor(memorySize/2);
+                memorySize = Math.floor(memorySize / 2);
             }
         }
 
@@ -67,19 +76,19 @@ export default async function builder(code, options) {
                 "memory": memory
             },
             runtime: {
-                exceptionHandler: function(code) {
+                exceptionHandler: function (code) {
                     let err;
-                    if (code == 1) {
+                    if (code === 1) {
                         err = "Signal not found. ";
-                    } else if (code == 2) {
+                    } else if (code === 2) {
                         err = "Too many signals set. ";
-                    } else if (code == 3) {
+                    } else if (code === 3) {
                         err = "Signal already set. ";
-                    } else if (code == 4) {
+                    } else if (code === 4) {
                         err = "Assert Failed. ";
-                    } else if (code == 5) {
+                    } else if (code === 5) {
                         err = "Not enough memory. ";
-                    } else if (code == 6) {
+                    } else if (code === 6) {
                         err = "Input signal array access exceeds the size. ";
                     } else {
                         err = "Unknown error. ";
@@ -89,10 +98,10 @@ export default async function builder(code, options) {
                 },
                 // A new way of logging messages was added in Circom 2.0.7 that requires 2 new imports
                 // `printErrorMessage` and `writeBufferMessage`.
-                printErrorMessage: function() {
+                printErrorMessage: function () {
                     errStr += getMessage() + "\n";
                 },
-                writeBufferMessage: function() {
+                writeBufferMessage: function () {
                     const msg = getMessage();
                     // Any calls to `log()` will always end with a `\n`, so that's when we print and reset
                     if (msg === "\n") {
@@ -101,17 +110,17 @@ export default async function builder(code, options) {
                     } else {
                         // If we've buffered other content, put a space in between the items
                         if (msgStr !== "") {
-                            msgStr += " "
+                            msgStr += " ";
                         }
                         // Then append the message to the message we are creating
                         msgStr += msg;
                     }
                 },
-                showSharedRWMemory: function() {
+                showSharedRWMemory: function () {
                     const shared_rw_memory_size = instance.exports.getFieldNumLen32();
                     const arr = new Uint32Array(shared_rw_memory_size);
-                    for (let j=0; j<shared_rw_memory_size; j++) {
-                        arr[shared_rw_memory_size-1-j] = instance.exports.readSharedRWMemory(j);
+                    for (let j = 0; j < shared_rw_memory_size; j++) {
+                        arr[shared_rw_memory_size - 1 - j] = instance.exports.readSharedRWMemory(j);
                     }
 
                     // In circom 2.0.7, they changed the log() function to allow strings and changed the
@@ -119,7 +128,7 @@ export default async function builder(code, options) {
                     if (majorVersion >= 2 && (minorVersion >= 1 || patchVersion >= 7)) {
                         // If we've buffered other content, put a space in between the items
                         if (msgStr !== "") {
-                            msgStr += " "
+                            msgStr += " ";
                         }
                         // Then append the value to the message we are creating
                         const msg = (Scalar.fromArray(arr, 0x100000000).toString());
@@ -128,39 +137,39 @@ export default async function builder(code, options) {
                         console.log(Scalar.fromArray(arr, 0x100000000));
                     }
                 },
-                error: function(code, pstr, a,b,c,d) {
+                error: function (code, pstr, a, b, c, d) {
                     let errStr;
-                    if (code == 7) {
-                        errStr=p2str(pstr) + " " + wc.getFr(b).toString() + " != " + wc.getFr(c).toString() + " " +p2str(d);
-                    } else if (code == 9) {
-                        errStr=p2str(pstr) + " " + wc.getFr(b).toString() + " " +p2str(c);
-                    } else if ((code == 5)&&(options.sym)) {
-                        errStr=p2str(pstr)+ " " + options.sym.labelIdx2Name[c];
+                    if (code === 7) {
+                        errStr = p2str(pstr) + " " + wc.getFr(b).toString() + " != " + wc.getFr(c).toString() + " " + p2str(d);
+                    } else if (code === 9) {
+                        errStr = p2str(pstr) + " " + wc.getFr(b).toString() + " " + p2str(c);
+                    } else if ((code === 5) && (options.sym)) {
+                        errStr = p2str(pstr) + " " + options.sym.labelIdx2Name[c];
                     } else {
-                        errStr=p2str(pstr)+ " " + a + " " + b + " " + c + " " + d;
+                        errStr = p2str(pstr) + " " + a + " " + b + " " + c + " " + d;
                     }
                     console.log("ERROR: ", code, errStr);
                     throw new Error(errStr);
                 },
-                log: function(a) {
+                log: function (a) {
                     console.log(wc.getFr(a).toString());
                 },
-                logGetSignal: function(signal, pVal) {
+                logGetSignal: function (signal, pVal) {
                     if (options.logGetSignal) {
-                        options.logGetSignal(signal, wc.getFr(pVal) );
+                        options.logGetSignal(signal, wc.getFr(pVal));
                     }
                 },
-                logSetSignal: function(signal, pVal) {
+                logSetSignal: function (signal, pVal) {
                     if (options.logSetSignal) {
-                        options.logSetSignal(signal, wc.getFr(pVal) );
+                        options.logSetSignal(signal, wc.getFr(pVal));
                     }
                 },
-                logStartComponent: function(cIdx) {
+                logStartComponent: function (cIdx) {
                     if (options.logStartComponent) {
                         options.logStartComponent(cIdx);
                     }
                 },
-                logFinishComponent: function(cIdx) {
+                logFinishComponent: function (cIdx) {
                     if (options.logFinishComponent) {
                         options.logFinishComponent(cIdx);
                     }
@@ -169,13 +178,13 @@ export default async function builder(code, options) {
         });
     }
 
-    if (typeof instance.exports.getVersion == 'function') {
+    if (typeof instance.exports.getVersion == "function") {
         majorVersion = instance.exports.getVersion();
     }
-    if (typeof instance.exports.getMinorVersion == 'function') {
+    if (typeof instance.exports.getMinorVersion == "function") {
         minorVersion = instance.exports.getMinorVersion();
     }
-    if (typeof instance.exports.getPatchVersion == 'function') {
+    if (typeof instance.exports.getPatchVersion == "function") {
         patchVersion = instance.exports.getPatchVersion();
     }
 
@@ -203,9 +212,9 @@ export default async function builder(code, options) {
     return wc;
 
     function getMessage() {
-        var message = "";
-        var c = instance.exports.getMessageChar();
-        while ( c != 0 ) {
+        let message = "";
+        let c = instance.exports.getMessageChar();
+        while (c !== 0) {
             message += String.fromCharCode(c);
             c = instance.exports.getMessageChar();
         }
@@ -217,11 +226,11 @@ export default async function builder(code, options) {
 
         const bytes = [];
 
-        for (let i=0; i8[p+i]>0; i++)  bytes.push(i8[p+i]);
+        for (let i = 0; i8[p + i] > 0; i++) bytes.push(i8[p + i]);
 
         return String.fromCharCode.apply(null, bytes);
     }
-};
+}
 
 class WitnessCalculatorCircom1 {
     constructor(memory, instance, sanityCheck) {
@@ -233,8 +242,8 @@ class WitnessCalculatorCircom1 {
         const pRawPrime = this.instance.exports.getPRawPrime();
 
         const arr = new Array(this.n32);
-        for (let i=0; i<this.n32; i++) {
-            arr[this.n32-1-i] = this.i32[(pRawPrime >> 2) + i];
+        for (let i = 0; i < this.n32; i++) {
+            arr[this.n32 - 1 - i] = this.i32[(pRawPrime >> 2) + i];
         }
 
         this.prime = Scalar.fromArray(arr, 0x100000000);
@@ -243,8 +252,8 @@ class WitnessCalculatorCircom1 {
 
         this.mask32 = Scalar.fromString("FFFFFFFF", 16);
         this.NVars = this.instance.exports.getNVars();
-        this.n64 = Math.floor((this.Fr.bitLength - 1) / 64)+1;
-        this.R = this.Fr.e( Scalar.shiftLeft(1 , this.n64*64));
+        this.n64 = Math.floor((this.Fr.bitLength - 1) / 64) + 1;
+        this.R = this.Fr.e(Scalar.shiftLeft(1, this.n64 * 64));
         this.RInv = this.Fr.inv(this.R);
         this.sanityCheck = sanityCheck;
     }
@@ -258,10 +267,10 @@ class WitnessCalculatorCircom1 {
         const pSigOffset = this.allocInt();
         const pFr = this.allocFr();
         const keys = Object.keys(input);
-        keys.forEach( (k) => {
+        keys.forEach((k) => {
             const h = fnvHash(k);
-            const hMSB = parseInt(h.slice(0,8), 16);
-            const hLSB = parseInt(h.slice(8,16), 16);
+            const hMSB = parseInt(h.slice(0, 8), 16);
+            const hLSB = parseInt(h.slice(8, 16), 16);
             try {
                 this.instance.exports.getSignalOffset32(pSigOffset, 0, hMSB, hLSB);
             } catch (err) {
@@ -269,7 +278,7 @@ class WitnessCalculatorCircom1 {
             }
             const sigOffset = this.getInt(pSigOffset);
             const fArr = flatArray(input[k]);
-            for (let i=0; i<fArr.length; i++) {
+            for (let i = 0; i < fArr.length; i++) {
                 this.setFr(pFr, fArr[i]);
                 this.instance.exports.setSignal(0, 0, sigOffset + i, pFr);
             }
@@ -284,7 +293,7 @@ class WitnessCalculatorCircom1 {
 
         await self._doCalculateWitness(input, sanityCheck);
 
-        for (let i=0; i<self.NVars; i++) {
+        for (let i = 0; i < self.NVars; i++) {
             const pWitness = self.instance.exports.getPWitness(i);
             w.push(self.getFr(pWitness));
         }
@@ -310,32 +319,32 @@ class WitnessCalculatorCircom1 {
 
     allocInt() {
         const p = this.i32[0];
-        this.i32[0] = p+8;
+        this.i32[0] = p + 8;
         return p;
     }
 
     allocFr() {
         const p = this.i32[0];
-        this.i32[0] = p+this.n32*4 + 8;
+        this.i32[0] = p + this.n32 * 4 + 8;
         return p;
     }
 
     getInt(p) {
-        return this.i32[p>>2];
+        return this.i32[p >> 2];
     }
 
     setInt(p, v) {
-        this.i32[p>>2] = v;
+        this.i32[p >> 2] = v;
     }
 
     getFr(p) {
         const self = this;
-        const idx = (p>>2);
+        const idx = (p >> 2);
 
         if (self.i32[idx + 1] & 0x80000000) {
             const arr = new Array(self.n32);
-            for (let i=0; i<self.n32; i++) {
-                arr[self.n32-1-i] = self.i32[idx+2+i];
+            for (let i = 0; i < self.n32; i++) {
+                arr[self.n32 - 1 - i] = self.i32[idx + 2 + i];
             }
             const res = self.Fr.e(Scalar.fromArray(arr, 0x100000000));
             if (self.i32[idx + 1] & 0x40000000) {
@@ -346,7 +355,7 @@ class WitnessCalculatorCircom1 {
 
         } else {
             if (self.i32[idx] & 0x80000000) {
-                return self.Fr.e( self.i32[idx] - 0x100000000);
+                return self.Fr.e(self.i32[idx] - 0x100000000);
             } else {
                 return self.Fr.e(self.i32[idx]);
             }
@@ -367,14 +376,13 @@ class WitnessCalculatorCircom1 {
         const minShort = self.Fr.neg(self.Fr.e("80000000", 16));
         const maxShort = self.Fr.e("7FFFFFFF", 16);
 
-        if (  (self.Fr.geq(v, minShort))
-            &&(self.Fr.leq(v, maxShort)))
-        {
+        if ((self.Fr.geq(v, minShort))
+            && (self.Fr.leq(v, maxShort))) {
             let a;
             if (self.Fr.geq(v, self.Fr.zero)) {
                 a = Scalar.toNumber(v);
             } else {
-                a = Scalar.toNumber( self.Fr.sub(v, minShort));
+                a = Scalar.toNumber(self.Fr.sub(v, minShort));
                 a = a - 0x80000000;
                 a = 0x100000000 + a;
             }
@@ -386,10 +394,10 @@ class WitnessCalculatorCircom1 {
         self.i32[(p >> 2)] = 0;
         self.i32[(p >> 2) + 1] = 0x80000000;
         const arr = Scalar.toArray(v, 0x100000000);
-        for (let i=0; i<self.n32; i++) {
-            const idx = arr.length-1-i;
+        for (let i = 0; i < self.n32; i++) {
+            const idx = arr.length - 1 - i;
 
-            if ( idx >=0) {
+            if (idx >= 0) {
                 self.i32[(p >> 2) + 2 + i] = arr[idx];
             } else {
                 self.i32[(p >> 2) + 2 + i] = 0;
@@ -407,8 +415,8 @@ class WitnessCalculatorCircom2 {
 
         this.instance.exports.getRawPrime();
         const arr = new Uint32Array(this.n32);
-        for (let i=0; i<this.n32; i++) {
-            arr[this.n32-1-i] = this.instance.exports.readSharedRWMemory(i);
+        for (let i = 0; i < this.n32; i++) {
+            arr[this.n32 - 1 - i] = this.instance.exports.readSharedRWMemory(i);
         }
         this.prime = Scalar.fromArray(arr, 0x100000000);
 
@@ -425,17 +433,17 @@ class WitnessCalculatorCircom2 {
         //input is assumed to be a map from signals to arrays of bigints
         this.instance.exports.init((this.sanityCheck || sanityCheck) ? 1 : 0);
         const keys = Object.keys(input);
-        var input_counter = 0;
-        keys.forEach( (k) => {
+        let input_counter = 0;
+        keys.forEach((k) => {
             const h = fnvHash(k);
-            const hMSB = parseInt(h.slice(0,8), 16);
-            const hLSB = parseInt(h.slice(8,16), 16);
+            const hMSB = parseInt(h.slice(0, 8), 16);
+            const hLSB = parseInt(h.slice(8, 16), 16);
             const fArr = flatArray(input[k]);
             // Slight deviation from https://github.com/iden3/circom/blob/v2.1.6/code_producers/src/wasm_elements/common/witness_calculator.js
             // because I don't know when this exported function was added
-            if (typeof this.instance.exports.getInputSignalSize === 'function') {
+            if (typeof this.instance.exports.getInputSignalSize === "function") {
                 let signalSize = this.instance.exports.getInputSignalSize(hMSB, hLSB);
-                if (signalSize < 0){
+                if (signalSize < 0) {
                     throw new Error(`Signal ${k} not found\n`);
                 }
                 if (fArr.length < signalSize) {
@@ -445,13 +453,13 @@ class WitnessCalculatorCircom2 {
                     throw new Error(`Too many values for input signal ${k}\n`);
                 }
             }
-            for (let i=0; i<fArr.length; i++) {
-                const arrFr = toArray32(normalize(fArr[i],this.prime),this.n32)
-                for (let j=0; j<this.n32; j++) {
-                    this.instance.exports.writeSharedRWMemory(j,arrFr[this.n32-1-j]);
+            for (let i = 0; i < fArr.length; i++) {
+                const arrFr = toArray32(normalize(fArr[i], this.prime), this.n32);
+                for (let j = 0; j < this.n32; j++) {
+                    this.instance.exports.writeSharedRWMemory(j, arrFr[this.n32 - 1 - j]);
                 }
                 try {
-                    this.instance.exports.setInputSignal(hMSB, hLSB,i);
+                    this.instance.exports.setInputSignal(hMSB, hLSB, i);
                     input_counter++;
                 } catch (err) {
                     // console.log(`After adding signal ${i} of ${k}`)
@@ -470,11 +478,11 @@ class WitnessCalculatorCircom2 {
 
         await this._doCalculateWitness(input, sanityCheck);
 
-        for (let i=0; i<this.witnessSize; i++) {
+        for (let i = 0; i < this.witnessSize; i++) {
             this.instance.exports.getWitness(i);
-        const arr = new Uint32Array(this.n32);
-            for (let j=0; j<this.n32; j++) {
-            arr[this.n32-1-j] = this.instance.exports.readSharedRWMemory(j);
+            const arr = new Uint32Array(this.n32);
+            for (let j = 0; j < this.n32; j++) {
+                arr[this.n32 - 1 - j] = this.instance.exports.readSharedRWMemory(j);
             }
             w.push(Scalar.fromArray(arr, 0x100000000));
         }
@@ -483,15 +491,15 @@ class WitnessCalculatorCircom2 {
     }
 
     async calculateWTNSBin(input, sanityCheck) {
-        const buff32 = new Uint32Array(this.witnessSize*this.n32+this.n32+11);
-        const buff = new  Uint8Array( buff32.buffer);
+        const buff32 = new Uint32Array(this.witnessSize * this.n32 + this.n32 + 11);
+        const buff = new Uint8Array(buff32.buffer);
         await this._doCalculateWitness(input, sanityCheck);
 
         //"wtns"
-        buff[0] = "w".charCodeAt(0)
-        buff[1] = "t".charCodeAt(0)
-        buff[2] = "n".charCodeAt(0)
-        buff[3] = "s".charCodeAt(0)
+        buff[0] = "w".charCodeAt(0);
+        buff[1] = "t".charCodeAt(0);
+        buff[2] = "n".charCodeAt(0);
+        buff[3] = "s".charCodeAt(0);
 
         //version 2
         buff32[1] = 2;
@@ -502,12 +510,12 @@ class WitnessCalculatorCircom2 {
         //id section 1
         buff32[3] = 1;
 
-        const n8 = this.n32*4;
+        const n8 = this.n32 * 4;
         //id section 1 length in 64bytes
         const idSection1length = 8 + n8;
         const idSection1lengthHex = idSection1length.toString(16);
-            buff32[4] = parseInt(idSection1lengthHex.slice(0,8), 16);
-            buff32[5] = parseInt(idSection1lengthHex.slice(8,16), 16);
+        buff32[4] = parseInt(idSection1lengthHex.slice(0, 8), 16);
+        buff32[5] = parseInt(idSection1lengthHex.slice(8, 16), 16);
 
         //this.n32
         buff32[6] = n8;
@@ -515,9 +523,9 @@ class WitnessCalculatorCircom2 {
         //prime number
         this.instance.exports.getRawPrime();
 
-        var pos = 7;
-        for (let j=0; j<this.n32; j++) {
-            buff32[pos+j] = this.instance.exports.readSharedRWMemory(j);
+        let pos = 7;
+        for (let j = 0; j < this.n32; j++) {
+            buff32[pos + j] = this.instance.exports.readSharedRWMemory(j);
         }
         pos += this.n32;
 
@@ -530,16 +538,16 @@ class WitnessCalculatorCircom2 {
         pos++;
 
         // section 2 length
-        const idSection2length = n8*this.witnessSize;
+        const idSection2length = n8 * this.witnessSize;
         const idSection2lengthHex = idSection2length.toString(16);
-        buff32[pos] = parseInt(idSection2lengthHex.slice(0,8), 16);
-        buff32[pos+1] = parseInt(idSection2lengthHex.slice(8,16), 16);
+        buff32[pos] = parseInt(idSection2lengthHex.slice(0, 8), 16);
+        buff32[pos + 1] = parseInt(idSection2lengthHex.slice(8, 16), 16);
 
         pos += 2;
-        for (let i=0; i<this.witnessSize; i++) {
+        for (let i = 0; i < this.witnessSize; i++) {
             this.instance.exports.getWitness(i);
-            for (let j=0; j<this.n32; j++) {
-                buff32[pos+j] = this.instance.exports.readSharedRWMemory(j);
+            for (let j = 0; j < this.n32; j++) {
+                buff32[pos + j] = this.instance.exports.readSharedRWMemory(j);
             }
             pos += this.n32;
         }