From 800b266bd826aca14490be7b527cd1da03498f1f Mon Sep 17 00:00:00 2001
From: Ryan Hendrickson <ryan.hendrickson@alum.mit.edu>
Date: Mon, 20 Nov 2017 13:37:13 -0500
Subject: [PATCH] refactor(lockfile): remove string concatenation from parsing
 code

Replace all instances of building strings incrementally using += with more efficient methods.
---
 src/lockfile/parse.js | 49 +++++++++++++++++++------------------------
 1 file changed, 22 insertions(+), 27 deletions(-)

diff --git a/src/lockfile/parse.js b/src/lockfile/parse.js
index 4db0830ac4..65ea9297bb 100644
--- a/src/lockfile/parse.js
+++ b/src/lockfile/parse.js
@@ -69,44 +69,43 @@ function* tokenise(input: string): Iterator<Token> {
     } else if (input[0] === '#') {
       chop++;
 
-      let val = '';
-      while (input[chop] !== '\n') {
-        val += input[chop];
-        chop++;
+      let nextNewline = input.indexOf('\n', chop);
+      if (nextNewline === -1) {
+        nextNewline = input.length;
       }
+      const val = input.substring(chop, nextNewline);
+      chop = nextNewline;
       yield buildToken(TOKEN_TYPES.comment, val);
     } else if (input[0] === ' ') {
       if (lastNewline) {
-        let indent = '';
-        for (let i = 0; input[i] === ' '; i++) {
-          indent += input[i];
+        let indentSize = 1;
+        for (let i = 1; input[i] === ' '; i++) {
+          indentSize++;
         }
 
-        if (indent.length % 2) {
+        if (indentSize % 2) {
           throw new TypeError('Invalid number of spaces');
         } else {
-          chop = indent.length;
-          yield buildToken(TOKEN_TYPES.indent, indent.length / 2);
+          chop = indentSize;
+          yield buildToken(TOKEN_TYPES.indent, indentSize / 2);
         }
       } else {
         chop++;
       }
     } else if (input[0] === '"') {
-      let val = '';
-
-      for (let i = 0; ; i++) {
-        const currentChar = input[i];
-        val += currentChar;
-
-        if (i > 0 && currentChar === '"') {
+      let i = 1;
+      for (; ; i++) {
+        if (input[i] === '"') {
           const isEscaped = input[i - 1] === '\\' && input[i - 2] !== '\\';
           if (!isEscaped) {
+            i++;
             break;
           }
         }
       }
+      const val = input.substring(0, i);
 
-      chop = val.length;
+      chop = i;
 
       try {
         yield buildToken(TOKEN_TYPES.string, JSON.parse(val));
@@ -118,10 +117,7 @@ function* tokenise(input: string): Iterator<Token> {
         }
       }
     } else if (/^[0-9]/.test(input)) {
-      let val = '';
-      for (let i = 0; /^[0-9]$/.test(input[i]); i++) {
-        val += input[i];
-      }
+      const val = /^[0-9]+/.exec(input)[0];
       chop = val.length;
 
       yield buildToken(TOKEN_TYPES.number, +val);
@@ -138,16 +134,15 @@ function* tokenise(input: string): Iterator<Token> {
       yield buildToken(TOKEN_TYPES.comma);
       chop++;
     } else if (/^[a-zA-Z\/-]/g.test(input)) {
-      let name = '';
-      for (let i = 0; i < input.length; i++) {
+      let i = 0;
+      for (; i < input.length; i++) {
         const char = input[i];
         if (char === ':' || char === ' ' || char === '\n' || char === '\r' || char === ',') {
           break;
-        } else {
-          name += char;
         }
       }
-      chop = name.length;
+      const name = input.substring(0, i);
+      chop = i;
 
       yield buildToken(TOKEN_TYPES.string, name);
     } else {