Substr

src/index.js

@@ -28,6 +28,48 @@ export function substring(str, begin = 0, end) {
     return str.match(astralRange).slice(begin, end).join("");
 }
 
+export function substr(str, begin = 0, len) {
+    // Check for input
+    if (typeof str !== "string") {
+        throw new Error("Input must be a string");
+    }
+
+    const strLength = length(str);
+
+    // Fix type
+    if (typeof begin !== "number") {
+        begin = parseInt(begin);
+    }
+
+    // Return zero-length string if got oversize number.
+    if(begin >= strLength){
+        return "";
+    }
+    // Calculating postive version of negative value.
+    else if(begin < 0) {
+        begin+= strLength;
+    }
+
+    let end = undefined;
+    if(typeof len === "undefined"){
+        end = strLength;
+    }
+    else {
+        // Fix type
+        if (typeof len !== "number"){
+            len = parseInt(len);
+        }
+        if (len >= 0) {
+            end = len + begin;
+        }
+        else{
+            end = begin;
+        }
+    }
+
+    return str.match(astralRange).slice(begin, end).join("");
+}
+
 export function limit(str, limit = 16, padString = "#", padPosition = "right") {
     // Input should be a string, limit should be a number
     if (typeof str !== "string" || typeof limit !== "number") {

test/substr.test.js

@@ -0,0 +1,34 @@
+import assert from "assert";
+import { substr } from "../src/index";
+
+describe("Substr", () => {
+    const string = "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe.";
+    const unicodeString = "دانشگاهی که دانشگاه نباشد، دانشگاه نیست.";
+    const emojiString = "Emojis 👍🏽 are 🍆 poison. 🌮s are bad.";
+
+    it("Substrs latin text correctly", () => {
+        assert.strictEqual(substr("Iñtërnâtiônàlizætiøn☃", 0, 10), "Iñtërnâtiô");
+        assert.strictEqual(substr(string, 25, 32), string.substr(25, 32));
+    });
+
+    it("Substrs unicode text correctly", () => {
+        assert.strictEqual(substr(unicodeString, 0, 11), "دانشگاهی که");
+        assert.strictEqual(substr(emojiString, 7, 7), "👍🏽 are 🍆");
+    });
+
+    it("Substrs if arguments are unspecified", () => {
+        assert.strictEqual(substr(string, 10), string.substr(10));
+        assert.strictEqual(substr(string, 120), string.substr(120));
+        assert.strictEqual(substr(string, '1', '2'), string.substr('1', '2'));
+        assert.strictEqual(substr(string), string);
+    });
+
+    it("Substrs even with negative arguments", () => {
+        assert.strictEqual(substr(string, -4), string.substr(-4));
+        assert.strictEqual(substr(string, -4, -1), string.substr(-4, -1));
+    });
+
+    it("Throws an error if wrong arguments are specified.", () => {
+        assert.throws(() => substr(12, 1, 2), Error);
+    });
+});