Use more for...of loops in the code-base

Note that these cases, which are all in older code, were found using the [`unicorn/no-for-loop`](https://github.com/sindresorhus/eslint-plugin-unicorn/blob/main/docs/rules/no-for-loop.md) ESLint plugin rule.
However, note that I've opted not to enable this rule by default since there's still *some* cases where I do think that it makes sense to allow "regular" for-loops.

extensions/chromium/extension-router.js

@@ -95,8 +95,8 @@ limitations under the License.
       url: CRX_BASE_URL + "*:*",
     },
     function (tabsFromLastSession) {
-      for (var i = 0; i < tabsFromLastSession.length; ++i) {
+      for (const { id } of tabsFromLastSession) {
-        chrome.tabs.reload(tabsFromLastSession[i].id);
+        chrome.tabs.reload(id);
       }
     }
   );

extensions/chromium/pdfHandler.js

@@ -54,8 +54,7 @@ function isPdfDownloadable(details) {
  * @returns {undefined|{name: string, value: string}} The header, if found.
  */
 function getHeaderFromHeaders(headers, headerName) {
-  for (var i = 0; i < headers.length; ++i) {
+  for (const header of headers) {
-    var header = headers[i];
     if (header.name.toLowerCase() === headerName) {
       return header;
     }

extensions/chromium/telemetry.js

@@ -110,8 +110,7 @@ limitations under the License.
       id = "";
       var buf = new Uint8Array(5);
       crypto.getRandomValues(buf);
-      for (var i = 0; i < buf.length; ++i) {
+      for (const c of buf) {
-        var c = buf[i];
         id += (c >>> 4).toString(16) + (c & 0xf).toString(16);
       }
       localStorage.telemetryDeduplicationId = id;

external/cmapscompress/compress.js

@@ -218,8 +218,8 @@ function parseCMap(binaryData) {
       const sign = fromHexDigit(num[num.length - 1]) & 1 ? 15 : 0;
       let c = 0;
       let result = "";
-      for (let i = 0; i < num.length; i++) {
+      for (const digit of num) {
-        c = (c << 4) | fromHexDigit(num[i]);
+        c = (c << 4) | fromHexDigit(digit);
         result += toHexDigit(sign ? (c >> 1) ^ sign : c >> 1);
         c &= 1;
       }

external/cmapscompress/optimize.js

@@ -196,13 +196,13 @@ exports.optimizeCMap = function (data) {
             i++;
             data.body.splice(i, 0, newItem);
           }
-          for (let j = 0; j < subitems.length; j++) {
+          for (const subitem of subitems) {
-            const code = subitems[j].code;
+            const { code } = subitem;
             let q = 0;
             while (q < groups.length && groups[q] <= code) {
               q++;
             }
-            buckets[q].push(subitems[j]);
+            buckets[q].push(subitem);
           }
         }
       }

gulpfile.js

@@ -782,8 +782,7 @@ gulp.task("locale", function () {
   subfolders.sort();
   let viewerOutput = "";
   const locales = [];
-  for (let i = 0; i < subfolders.length; i++) {
+  for (const locale of subfolders) {
-    const locale = subfolders[i];
     const dirPath = L10N_DIR + locale;
     if (!checkDir(dirPath)) {
       continue;

src/core/cff_parser.js

@@ -1682,9 +1682,7 @@ class CFFCompiler {
   compileDict(dict, offsetTracker) {
     const out = [];
     // The dictionary keys must be in a certain order.
-    const order = dict.order;
+    for (const key of dict.order) {
-    for (let i = 0; i < order.length; ++i) {
-      const key = order[i];
       if (!(key in dict.values)) {
         continue;
       }

src/core/type1_font.js

@@ -219,9 +219,8 @@ class Type1Font {
 
   getCharset() {
     const charset = [".notdef"];
-    const charstrings = this.charstrings;
+    for (const { glyphName } of this.charstrings) {
-    for (let glyphId = 0; glyphId < charstrings.length; glyphId++) {
+      charset.push(glyphName);
-      charset.push(charstrings[glyphId].glyphName);
     }
     return charset;
   }

src/core/type1_parser.js

@@ -576,7 +576,7 @@ const Type1Parser = (function Type1ParserClosure() {
           privateData,
         },
       };
-      let token, length, data, lenIV, encoded;
+      let token, length, data, lenIV;
       while ((token = this.getToken()) !== null) {
         if (token !== "/") {
           continue;
@@ -604,7 +604,7 @@ const Type1Parser = (function Type1ParserClosure() {
               this.getToken(); // read in 'RD' or '-|'
               data = length > 0 ? stream.getBytes(length) : new Uint8Array(0);
               lenIV = program.properties.privateData.lenIV;
-              encoded = this.readCharStrings(data, lenIV);
+              const encoded = this.readCharStrings(data, lenIV);
               this.nextChar();
               token = this.getToken(); // read in 'ND' or '|-'
               if (token === "noaccess") {
@@ -629,7 +629,7 @@ const Type1Parser = (function Type1ParserClosure() {
               this.getToken(); // read in 'RD' or '-|'
               data = length > 0 ? stream.getBytes(length) : new Uint8Array(0);
               lenIV = program.properties.privateData.lenIV;
-              encoded = this.readCharStrings(data, lenIV);
+              const encoded = this.readCharStrings(data, lenIV);
               this.nextChar();
               token = this.getToken(); // read in 'NP' or '|'
               if (token === "noaccess") {
@@ -675,9 +675,7 @@ const Type1Parser = (function Type1ParserClosure() {
         }
       }
 
-      for (let i = 0; i < charstrings.length; i++) {
+      for (const { encoded, glyph } of charstrings) {
-        const glyph = charstrings[i].glyph;
-        encoded = charstrings[i].encoded;
         const charString = new Type1CharString();
         const error = charString.convert(
           encoded,

src/core/worker.js

@@ -263,8 +263,8 @@ class WorkerMessageHandler {
           // There may be a chance that `newPdfManager` is not initialized for
           // the first few runs of `readchunk` block of code. Be sure to send
           // all cached chunks, if any, to chunked_stream via pdf_manager.
-          for (let i = 0; i < cachedChunks.length; i++) {
+          for (const chunk of cachedChunks) {
-            newPdfManager.sendProgressiveData(cachedChunks[i]);
+            newPdfManager.sendProgressiveData(chunk);
           }
 
           cachedChunks = [];

src/display/canvas.js

@@ -2211,8 +2211,7 @@ class CanvasGraphics {
 
     ctx.save();
     ctx.beginPath();
-    for (let i = 0; i < paths.length; i++) {
+    for (const path of paths) {
-      const path = paths[i];
       ctx.setTransform.apply(ctx, path.transform);
       ctx.translate(path.x, path.y);
       path.addToPath(ctx, path.fontSize);

test/resources/reftest-analyzer.js

@@ -301,8 +301,8 @@ window.onload = function () {
 
     // Bind an event handler to each image link
     const images = document.getElementsByClassName("image");
-    for (let i = 0; i < images.length; i++) {
+    for (const image of images) {
-      images[i].addEventListener(
+      image.addEventListener(
         "click",
         function (e) {
           showImages(e.target.id);
@@ -407,9 +407,9 @@ window.onload = function () {
   function flashPixels(on) {
     const stroke = on ? "#FF0000" : "#CCC";
     const strokeWidth = on ? "2px" : "1px";
-    for (let i = 0; i < gFlashingPixels.length; i++) {
+    for (const pixel of gFlashingPixels) {
-      gFlashingPixels[i].setAttribute("stroke", stroke);
+      pixel.setAttribute("stroke", stroke);
-      gFlashingPixels[i].setAttribute("stroke-width", strokeWidth);
+      pixel.setAttribute("stroke-width", strokeWidth);
     }
   }
 

test/stats/statcmp.js

@@ -30,17 +30,13 @@ function parseOptions() {
 
 function group(stats, groupBy) {
   const vals = [];
-  for (let i = 0; i < stats.length; i++) {
+  for (const curStat of stats) {
-    const curStat = stats[i];
     const keyArr = [];
-    for (let j = 0; j < groupBy.length; j++) {
+    for (const entry of groupBy) {
-      keyArr.push(curStat[groupBy[j]]);
+      keyArr.push(curStat[entry]);
     }
     const key = keyArr.join(",");
-    if (vals[key] === undefined) {
+    (vals[key] ||= []).push(curStat.time);
-      vals[key] = [];
-    }
-    vals[key].push(curStat.time);
   }
   return vals;
 }
@@ -134,8 +130,7 @@ function stat(baseline, current) {
     return s.length;
   });
   rows.push(labels);
-  for (let k = 0; k < keys.length; k++) {
+  for (const key of keys) {
-    const key = keys[k];
     const baselineMean = mean(baselineGroup[key]);
     const currentMean = mean(currentGroup[key]);
     const row = key.split(",");
@@ -172,8 +167,7 @@ function stat(baseline, current) {
   // print output
   console.log("-- Grouped By " + options.groupBy.join(", ") + " --");
   const groupCount = options.groupBy.length;
-  for (let r = 0; r < rows.length; r++) {
+  for (const row of rows) {
-    const row = rows[r];
     for (let i = 0; i < row.length; i++) {
       row[i] = pad(row[i], width[i], i < groupCount ? "right" : "left");
     }

test/unit/function_spec.js

@@ -416,10 +416,10 @@ describe("function", function () {
           "destOffset",
           compiledCode
         );
-        for (let i = 0; i < samples.length; i++) {
+        for (const { input, output } of samples) {
-          const out = new Float32Array(samples[i].output.length);
+          const out = new Float32Array(output.length);
-          fn(samples[i].input, 0, out, 0);
+          fn(input, 0, out, 0);
-          expect(Array.prototype.slice.call(out, 0)).toEqual(samples[i].output);
+          expect(Array.prototype.slice.call(out, 0)).toEqual(output);
         }
       }
     }