perf: dump isNaN; it is very costly

lib/saxes.js

@@ -632,13 +632,18 @@ class SaxesParser {
   getCode10() {
     const { chunk, i } = this;
     this.prevI = i;
+    // Yes, we do this instead of doing this.i++. Doing it this way, we do not
+    // read this.i again, which is a bit faster.
+    this.i = i + 1;
+
+    if (i >= chunk.length) {
+      return undefined;
+    }
+
     // Using charCodeAt and handling the surrogates ourselves is faster
     // than using codePointAt.
     const code = chunk.charCodeAt(i);
 
-    // Yes, we do this instead of doing this.i++. Doing it this way, we do not
-    // read this.i again, which is a bit faster.
-    this.i = i + 1;
     if (code < 0xD800) {
       if (code >= SPACE || code === TAB) {
         return code;
@@ -679,11 +684,6 @@ class SaxesParser {
       return code;
     }
 
-    // eslint-disable-next-line no-restricted-globals
-    if (isNaN(code)) {
-      return undefined;
-    }
-
     const final = 0x10000 + ((code - 0xD800) * 0x400) +
           (chunk.charCodeAt(i + 1) - 0xDC00);
     this.i = i + 2;
@@ -711,13 +711,18 @@ class SaxesParser {
   getCode11() {
     const { chunk, i } = this;
     this.prevI = i;
+    // Yes, we do this instead of doing this.i++. Doing it this way, we do not
+    // read this.i again, which is a bit faster.
+    this.i = i + 1;
+
+    if (i >= chunk.length) {
+      return undefined;
+    }
+
     // Using charCodeAt and handling the surrogates ourselves is faster
     // than using codePointAt.
     const code = chunk.charCodeAt(i);
 
-    // Yes, we do this instead of doing this.i++. Doing it this way, we do not
-    // read this.i again, which is a bit faster.
-    this.i = i + 1;
     if (code < 0xD800) {
       if ((code > 0x1F && code < 0x7F) || (code > 0x9F && code !== LS) ||
           code === TAB) {
@@ -761,11 +766,6 @@ class SaxesParser {
       return code;
     }
 
-    // eslint-disable-next-line no-restricted-globals
-    if (isNaN(code)) {
-      return undefined;
-    }
-
     const final = 0x10000 + ((code - 0xD800) * 0x400) +
           (chunk.charCodeAt(i + 1) - 0xDC00);
     this.i = i + 2;