diff --git a/src/core/chunked_stream.js b/src/core/chunked_stream.js
index 4cc41bf20..7cd136994 100644
--- a/src/core/chunked_stream.js
+++ b/src/core/chunked_stream.js
@@ -519,15 +519,15 @@ class ChunkedStreamManager {
     }
 
     const loadedRequests = [];
-    for (let chunk = beginChunk; chunk < endChunk; ++chunk) {
+    for (let curChunk = beginChunk; curChunk < endChunk; ++curChunk) {
       // The server might return more chunks than requested.
-      const requestIds = this.requestsByChunk[chunk] || [];
-      delete this.requestsByChunk[chunk];
+      const requestIds = this.requestsByChunk[curChunk] || [];
+      delete this.requestsByChunk[curChunk];
 
       for (const requestId of requestIds) {
         const chunksNeeded = this.chunksNeededByRequest[requestId];
-        if (chunk in chunksNeeded) {
-          delete chunksNeeded[chunk];
+        if (curChunk in chunksNeeded) {
+          delete chunksNeeded[curChunk];
         }
 
         if (!isEmptyObj(chunksNeeded)) {
diff --git a/src/core/document.js b/src/core/document.js
index 32ea4740a..42532db16 100644
--- a/src/core/document.js
+++ b/src/core/document.js
@@ -216,8 +216,8 @@ class Page {
       // Fetching the individual streams from the array.
       const xref = this.xref;
       const streams = [];
-      for (const stream of content) {
-        streams.push(xref.fetchIfRef(stream));
+      for (const subStream of content) {
+        streams.push(xref.fetchIfRef(subStream));
       }
       stream = new StreamsSequenceStream(streams);
     } else if (isStream(content)) {
diff --git a/src/core/evaluator.js b/src/core/evaluator.js
index 5d84b3844..7b4cd114a 100644
--- a/src/core/evaluator.js
+++ b/src/core/evaluator.js
@@ -629,7 +629,7 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
         pdfFunctionFactory: this.pdfFunctionFactory,
       })
         .then(imageObj => {
-          var imgData = imageObj.createImageData(/* forceRGBA = */ false);
+          imgData = imageObj.createImageData(/* forceRGBA = */ false);
 
           if (this.parsingType3Font) {
             return this.handler.sendWithPromise(
@@ -2479,16 +2479,16 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
       properties.hasEncoding = !!baseEncodingName || differences.length > 0;
       properties.dict = dict;
       return toUnicodePromise
-        .then(toUnicode => {
-          properties.toUnicode = toUnicode;
+        .then(readToUnicode => {
+          properties.toUnicode = readToUnicode;
           return this.buildToUnicode(properties);
         })
-        .then(toUnicode => {
-          properties.toUnicode = toUnicode;
+        .then(builtToUnicode => {
+          properties.toUnicode = builtToUnicode;
           if (cidToGidBytes) {
             properties.cidToGidMap = this.readCidToGidMap(
               cidToGidBytes,
-              toUnicode
+              builtToUnicode
             );
           }
           return properties;
@@ -3092,21 +3092,21 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
           };
           const widths = dict.get("Widths");
           return this.extractDataStructures(dict, dict, properties).then(
-            properties => {
+            newProperties => {
               if (widths) {
                 const glyphWidths = [];
                 let j = firstChar;
                 for (let i = 0, ii = widths.length; i < ii; i++) {
                   glyphWidths[j++] = this.xref.fetchIfRef(widths[i]);
                 }
-                properties.widths = glyphWidths;
+                newProperties.widths = glyphWidths;
               } else {
-                properties.widths = this.buildCharCodeToWidth(
+                newProperties.widths = this.buildCharCodeToWidth(
                   metrics.widths,
-                  properties
+                  newProperties
                 );
               }
-              return new Font(baseFontName, null, properties);
+              return new Font(baseFontName, null, newProperties);
             }
           );
         }
@@ -3212,13 +3212,13 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
         .then(() => {
           return this.extractDataStructures(dict, baseDict, properties);
         })
-        .then(properties => {
-          this.extractWidths(dict, descriptor, properties);
+        .then(newProperties => {
+          this.extractWidths(dict, descriptor, newProperties);
 
           if (type === "Type3") {
-            properties.isType3Font = true;
+            newProperties.isType3Font = true;
           }
-          return new Font(fontName.name, fontFile, properties);
+          return new Font(fontName.name, fontFile, newProperties);
         });
     },
   };
@@ -3352,8 +3352,8 @@ var TranslatedFont = (function TranslatedFontClosure() {
             })
             .catch(function(reason) {
               warn(`Type3 font resource "${key}" is not available.`);
-              var operatorList = new OperatorList();
-              charProcOperatorList[key] = operatorList.getIR();
+              const dummyOperatorList = new OperatorList();
+              charProcOperatorList[key] = dummyOperatorList.getIR();
             });
         });
       }
diff --git a/src/core/font_renderer.js b/src/core/font_renderer.js
index 03599d635..b09c18a81 100644
--- a/src/core/font_renderer.js
+++ b/src/core/font_renderer.js
@@ -345,12 +345,7 @@ var FontRendererFactory = (function FontRendererFactoryClosure() {
     }
   }
 
-  function compileCharString(code, cmds, font, glyphId) {
-    var stack = [];
-    var x = 0,
-      y = 0;
-    var stems = 0;
-
+  function compileCharString(charStringCode, cmds, font, glyphId) {
     function moveTo(x, y) {
       cmds.push({ cmd: "moveTo", args: [x, y] });
     }
@@ -361,6 +356,11 @@ var FontRendererFactory = (function FontRendererFactoryClosure() {
       cmds.push({ cmd: "bezierCurveTo", args: [x1, y1, x2, y2, x, y] });
     }
 
+    var stack = [];
+    var x = 0,
+      y = 0;
+    var stems = 0;
+
     function parse(code) {
       var i = 0;
       while (i < code.length) {
@@ -719,7 +719,7 @@ var FontRendererFactory = (function FontRendererFactoryClosure() {
         }
       }
     }
-    parse(code);
+    parse(charStringCode);
   }
 
   const NOOP = [];
diff --git a/src/core/fonts.js b/src/core/fonts.js
index 614048c9a..e69ff3970 100644
--- a/src/core/fonts.js
+++ b/src/core/fonts.js
@@ -1269,7 +1269,6 @@ var Font = (function FontClosure() {
 
     fallbackToSystemFont: function Font_fallbackToSystemFont() {
       this.missingFile = true;
-      var charCode, unicode;
       // The file data is not specified. Trying to fix the font name
       // to be used with the canvas.font.
       var name = this.name;
@@ -1303,17 +1302,17 @@ var Font = (function FontClosure() {
         // Standard fonts might be embedded as CID font without glyph mapping.
         // Building one based on GlyphMapForStandardFonts.
         const map = [];
-        for (charCode in GlyphMapForStandardFonts) {
+        for (const charCode in GlyphMapForStandardFonts) {
           map[+charCode] = GlyphMapForStandardFonts[charCode];
         }
         if (/Arial-?Black/i.test(name)) {
           var SupplementalGlyphMapForArialBlack = getSupplementalGlyphMapForArialBlack();
-          for (charCode in SupplementalGlyphMapForArialBlack) {
+          for (const charCode in SupplementalGlyphMapForArialBlack) {
             map[+charCode] = SupplementalGlyphMapForArialBlack[charCode];
           }
         } else if (/Calibri/i.test(name)) {
           const SupplementalGlyphMapForCalibri = getSupplementalGlyphMapForCalibri();
-          for (charCode in SupplementalGlyphMapForCalibri) {
+          for (const charCode in SupplementalGlyphMapForCalibri) {
             map[+charCode] = SupplementalGlyphMapForCalibri[charCode];
           }
         }
@@ -1354,7 +1353,7 @@ var Font = (function FontClosure() {
           if (!this.composite) {
             var glyphName =
               this.differences[charCode] || this.defaultEncoding[charCode];
-            unicode = getUnicodeForGlyph(glyphName, glyphsUnicodeMap);
+            const unicode = getUnicodeForGlyph(glyphName, glyphsUnicodeMap);
             if (unicode !== -1) {
               unicodeCharCode = unicode;
             }
@@ -1368,7 +1367,7 @@ var Font = (function FontClosure() {
           if (/Verdana/i.test(name)) {
             // Fixes issue11242_reduced.pdf
             const GlyphMapForStandardFonts = getGlyphMapForStandardFonts();
-            for (charCode in GlyphMapForStandardFonts) {
+            for (const charCode in GlyphMapForStandardFonts) {
               map[+charCode] = GlyphMapForStandardFonts[charCode];
             }
           }
@@ -1409,7 +1408,7 @@ var Font = (function FontClosure() {
         tables["post"] = null;
 
         for (let i = 0; i < numTables; i++) {
-          const table = readTableEntry(font);
+          const table = readTableEntry(file);
           if (!VALID_TABLES.includes(table.tag)) {
             continue; // skipping table if it's not a required or optional table
           }
@@ -1529,7 +1528,7 @@ var Font = (function FontClosure() {
        * Read the appropriate subtable from the cmap according to 9.6.6.4 from
        * PDF spec
        */
-      function readCmapTable(cmap, font, isSymbolicFont, hasEncoding) {
+      function readCmapTable(cmap, file, isSymbolicFont, hasEncoding) {
         if (!cmap) {
           warn("No cmap table available.");
           return {
@@ -1540,11 +1539,11 @@ var Font = (function FontClosure() {
           };
         }
         var segment;
-        var start = (font.start ? font.start : 0) + cmap.offset;
-        font.pos = start;
+        var start = (file.start ? file.start : 0) + cmap.offset;
+        file.pos = start;
 
-        font.getUint16(); // version
-        var numTables = font.getUint16();
+        file.getUint16(); // version
+        var numTables = file.getUint16();
 
         var potentialTable;
         var canBreak = false;
@@ -1555,9 +1554,9 @@ var Font = (function FontClosure() {
         // The following takes advantage of the fact that the tables are sorted
         // to work.
         for (var i = 0; i < numTables; i++) {
-          var platformId = font.getUint16();
-          var encodingId = font.getUint16();
-          var offset = font.getInt32() >>> 0;
+          var platformId = file.getUint16();
+          var encodingId = file.getUint16();
+          var offset = file.getInt32() >>> 0;
           var useTable = false;
 
           // Sometimes there are multiple of the same type of table. Default
@@ -1605,9 +1604,9 @@ var Font = (function FontClosure() {
         }
 
         if (potentialTable) {
-          font.pos = start + potentialTable.offset;
+          file.pos = start + potentialTable.offset;
         }
-        if (!potentialTable || font.peekByte() === -1) {
+        if (!potentialTable || file.peekByte() === -1) {
           warn("Could not find a preferred cmap table.");
           return {
             platformId: -1,
@@ -1617,9 +1616,9 @@ var Font = (function FontClosure() {
           };
         }
 
-        var format = font.getUint16();
-        font.getUint16(); // length
-        font.getUint16(); // language
+        var format = file.getUint16();
+        file.getUint16(); // length
+        file.getUint16(); // language
 
         var hasShortCmap = false;
         var mappings = [];
@@ -1628,7 +1627,7 @@ var Font = (function FontClosure() {
         // TODO(mack): refactor this cmap subtable reading logic out
         if (format === 0) {
           for (j = 0; j < 256; j++) {
-            var index = font.getByte();
+            var index = file.getByte();
             if (!index) {
               continue;
             }
@@ -1641,26 +1640,26 @@ var Font = (function FontClosure() {
         } else if (format === 4) {
           // re-creating the table in format 4 since the encoding
           // might be changed
-          var segCount = font.getUint16() >> 1;
-          font.getBytes(6); // skipping range fields
+          var segCount = file.getUint16() >> 1;
+          file.getBytes(6); // skipping range fields
           var segIndex,
             segments = [];
           for (segIndex = 0; segIndex < segCount; segIndex++) {
-            segments.push({ end: font.getUint16() });
+            segments.push({ end: file.getUint16() });
           }
-          font.getUint16();
+          file.getUint16();
           for (segIndex = 0; segIndex < segCount; segIndex++) {
-            segments[segIndex].start = font.getUint16();
+            segments[segIndex].start = file.getUint16();
           }
 
           for (segIndex = 0; segIndex < segCount; segIndex++) {
-            segments[segIndex].delta = font.getUint16();
+            segments[segIndex].delta = file.getUint16();
           }
 
           var offsetsCount = 0;
           for (segIndex = 0; segIndex < segCount; segIndex++) {
             segment = segments[segIndex];
-            var rangeOffset = font.getUint16();
+            var rangeOffset = file.getUint16();
             if (!rangeOffset) {
               segment.offsetIndex = -1;
               continue;
@@ -1676,7 +1675,7 @@ var Font = (function FontClosure() {
 
           var offsets = [];
           for (j = 0; j < offsetsCount; j++) {
-            offsets.push(font.getUint16());
+            offsets.push(file.getUint16());
           }
 
           for (segIndex = 0; segIndex < segCount; segIndex++) {
@@ -1705,11 +1704,11 @@ var Font = (function FontClosure() {
           // table. (This looks weird, so I can have missed something), this
           // works on Linux but seems to fails on Mac so let's rewrite the
           // cmap table to a 3-1-4 style
-          var firstCode = font.getUint16();
-          var entryCount = font.getUint16();
+          var firstCode = file.getUint16();
+          var entryCount = file.getUint16();
 
           for (j = 0; j < entryCount; j++) {
-            glyphId = font.getUint16();
+            glyphId = file.getUint16();
             var charCode = firstCode + j;
 
             mappings.push({
@@ -1747,7 +1746,7 @@ var Font = (function FontClosure() {
       }
 
       function sanitizeMetrics(
-        font,
+        file,
         header,
         metrics,
         numGlyphs,
@@ -1760,21 +1759,21 @@ var Font = (function FontClosure() {
           return;
         }
 
-        font.pos = (font.start ? font.start : 0) + header.offset;
-        font.pos += 4; // version
-        font.pos += 2; // ascent
-        font.pos += 2; // descent
-        font.pos += 2; // linegap
-        font.pos += 2; // adv_width_max
-        font.pos += 2; // min_sb1
-        font.pos += 2; // min_sb2
-        font.pos += 2; // max_extent
-        font.pos += 2; // caret_slope_rise
-        font.pos += 2; // caret_slope_run
-        font.pos += 2; // caret_offset
-        font.pos += 8; // reserved
-        font.pos += 2; // format
-        var numOfMetrics = font.getUint16();
+        file.pos = (file.start ? file.start : 0) + header.offset;
+        file.pos += 4; // version
+        file.pos += 2; // ascent
+        file.pos += 2; // descent
+        file.pos += 2; // linegap
+        file.pos += 2; // adv_width_max
+        file.pos += 2; // min_sb1
+        file.pos += 2; // min_sb2
+        file.pos += 2; // max_extent
+        file.pos += 2; // caret_slope_rise
+        file.pos += 2; // caret_slope_run
+        file.pos += 2; // caret_offset
+        file.pos += 8; // reserved
+        file.pos += 2; // format
+        var numOfMetrics = file.getUint16();
 
         if (numOfMetrics > numGlyphs) {
           info(
@@ -2107,7 +2106,7 @@ var Font = (function FontClosure() {
         };
       }
 
-      function readPostScriptTable(post, properties, maxpNumGlyphs) {
+      function readPostScriptTable(post, propertiesObj, maxpNumGlyphs) {
         var start = (font.start ? font.start : 0) + post.offset;
         font.pos = start;
 
@@ -2168,12 +2167,12 @@ var Font = (function FontClosure() {
           default:
             warn("Unknown/unsupported post table version " + version);
             valid = false;
-            if (properties.defaultEncoding) {
-              glyphNames = properties.defaultEncoding;
+            if (propertiesObj.defaultEncoding) {
+              glyphNames = propertiesObj.defaultEncoding;
             }
             break;
         }
-        properties.glyphNames = glyphNames;
+        propertiesObj.glyphNames = glyphNames;
         return valid;
       }
 
@@ -2706,8 +2705,7 @@ var Font = (function FontClosure() {
         data: createPostTable(properties),
       };
 
-      var charCodeToGlyphId = [],
-        charCode;
+      const charCodeToGlyphId = [];
 
       // Helper function to try to skip mapping of empty glyphs.
       function hasGlyph(glyphId) {
@@ -2773,7 +2771,7 @@ var Font = (function FontClosure() {
             baseEncoding = getEncoding(properties.baseEncodingName);
           }
           var glyphsUnicodeMap = getGlyphsUnicode();
-          for (charCode = 0; charCode < 256; charCode++) {
+          for (let charCode = 0; charCode < 256; charCode++) {
             var glyphName, standardGlyphName;
             if (this.differences && charCode in this.differences) {
               glyphName = this.differences[charCode];
@@ -2840,7 +2838,7 @@ var Font = (function FontClosure() {
           // (e.g. 0x2013) which when masked would overwrite other values in the
           // cmap.
           for (let i = 0; i < cmapMappingsLength; ++i) {
-            charCode = cmapMappings[i].charCode;
+            let charCode = cmapMappings[i].charCode;
             if (
               cmapPlatformId === 3 &&
               charCode >= 0xf000 &&
@@ -3000,7 +2998,7 @@ var Font = (function FontClosure() {
             // to begin with.
             continue;
           }
-          for (var i = 0, ii = charCodes.length; i < ii; i++) {
+          for (let i = 0, ii = charCodes.length; i < ii; i++) {
             var charCode = charCodes[i];
             // Find a fontCharCode that maps to the base and accent glyphs.
             // If one doesn't exists, create it.
@@ -3089,7 +3087,7 @@ var Font = (function FontClosure() {
           var charstrings = font.charstrings;
           var cffWidths = font.cff ? font.cff.widths : null;
           var hmtx = "\x00\x00\x00\x00"; // Fake .notdef
-          for (var i = 1, ii = numGlyphs; i < ii; i++) {
+          for (let i = 1, ii = numGlyphs; i < ii; i++) {
             var width = 0;
             if (charstrings) {
               var charstring = charstrings[i - 1];
@@ -3564,8 +3562,8 @@ var Type1Font = (function Type1FontClosure() {
       SEAC_ANALYSIS_ENABLED
     );
     var data = eexecBlockParser.extractFontProgram(properties);
-    for (var info in data.properties) {
-      properties[info] = data.properties[info];
+    for (const key in data.properties) {
+      properties[key] = data.properties[key];
     }
 
     var charstrings = data.charstrings;
diff --git a/src/core/function.js b/src/core/function.js
index 029058b43..c919d3e31 100644
--- a/src/core/function.js
+++ b/src/core/function.js
@@ -55,8 +55,8 @@ function toNumberArray(arr) {
     if (typeof arr[i] !== "number") {
       // Non-number is found -- convert all items to numbers.
       const result = new Array(length);
-      for (let i = 0; i < length; i++) {
-        result[i] = +arr[i];
+      for (let j = 0; j < length; j++) {
+        result[j] = +arr[j];
       }
       return result;
     }
@@ -1088,18 +1088,17 @@ var PostScriptCompiler = (function PostScriptCompilerClosure() {
   PostScriptCompiler.prototype = {
     compile: function PostScriptCompiler_compile(code, domain, range) {
       var stack = [];
-      var i, ii;
       var instructions = [];
       var inputSize = domain.length >> 1,
         outputSize = range.length >> 1;
       var lastRegister = 0;
       var n, j;
       var num1, num2, ast1, ast2, tmpVar, item;
-      for (i = 0; i < inputSize; i++) {
+      for (let i = 0; i < inputSize; i++) {
         stack.push(new AstArgument(i, domain[i * 2], domain[i * 2 + 1]));
       }
 
-      for (i = 0, ii = code.length; i < ii; i++) {
+      for (let i = 0, ii = code.length; i < ii; i++) {
         item = code[i];
         if (typeof item === "number") {
           stack.push(new AstLiteral(item));
diff --git a/src/core/jpg.js b/src/core/jpg.js
index b80739a7d..7214abe96 100644
--- a/src/core/jpg.js
+++ b/src/core/jpg.js
@@ -223,10 +223,10 @@ var JpegImage = (function JpegImageClosure() {
       return n + (-1 << length) + 1;
     }
 
-    function decodeBaseline(component, offset) {
+    function decodeBaseline(component, blockOffset) {
       var t = decodeHuffman(component.huffmanTableDC);
       var diff = t === 0 ? 0 : receiveAndExtend(t);
-      component.blockData[offset] = component.pred += diff;
+      component.blockData[blockOffset] = component.pred += diff;
       var k = 1;
       while (k < 64) {
         var rs = decodeHuffman(component.huffmanTableAC);
@@ -241,23 +241,23 @@ var JpegImage = (function JpegImageClosure() {
         }
         k += r;
         var z = dctZigZag[k];
-        component.blockData[offset + z] = receiveAndExtend(s);
+        component.blockData[blockOffset + z] = receiveAndExtend(s);
         k++;
       }
     }
 
-    function decodeDCFirst(component, offset) {
+    function decodeDCFirst(component, blockOffset) {
       var t = decodeHuffman(component.huffmanTableDC);
       var diff = t === 0 ? 0 : receiveAndExtend(t) << successive;
-      component.blockData[offset] = component.pred += diff;
+      component.blockData[blockOffset] = component.pred += diff;
     }
 
-    function decodeDCSuccessive(component, offset) {
-      component.blockData[offset] |= readBit() << successive;
+    function decodeDCSuccessive(component, blockOffset) {
+      component.blockData[blockOffset] |= readBit() << successive;
     }
 
     var eobrun = 0;
-    function decodeACFirst(component, offset) {
+    function decodeACFirst(component, blockOffset) {
       if (eobrun > 0) {
         eobrun--;
         return;
@@ -278,7 +278,7 @@ var JpegImage = (function JpegImageClosure() {
         }
         k += r;
         var z = dctZigZag[k];
-        component.blockData[offset + z] =
+        component.blockData[blockOffset + z] =
           receiveAndExtend(s) * (1 << successive);
         k++;
       }
@@ -286,14 +286,14 @@ var JpegImage = (function JpegImageClosure() {
 
     var successiveACState = 0,
       successiveACNextValue;
-    function decodeACSuccessive(component, offset) {
+    function decodeACSuccessive(component, blockOffset) {
       var k = spectralStart;
       var e = spectralEnd;
       var r = 0;
       var s;
       var rs;
       while (k <= e) {
-        const offsetZ = offset + dctZigZag[k];
+        const offsetZ = blockOffset + dctZigZag[k];
         const sign = component.blockData[offsetZ] < 0 ? -1 : 1;
         switch (successiveACState) {
           case 0: // initial state
@@ -358,15 +358,15 @@ var JpegImage = (function JpegImageClosure() {
       var mcuCol = mcu % mcusPerLine;
       blockRow = mcuRow * component.v + row;
       var blockCol = mcuCol * component.h + col;
-      var offset = getBlockBufferOffset(component, blockRow, blockCol);
-      decode(component, offset);
+      const blockOffset = getBlockBufferOffset(component, blockRow, blockCol);
+      decode(component, blockOffset);
     }
 
     function decodeBlock(component, decode, mcu) {
       blockRow = (mcu / component.blocksPerLine) | 0;
       var blockCol = mcu % component.blocksPerLine;
-      var offset = getBlockBufferOffset(component, blockRow, blockCol);
-      decode(component, offset);
+      const blockOffset = getBlockBufferOffset(component, blockRow, blockCol);
+      decode(component, blockOffset);
     }
 
     var componentsLength = components.length;
diff --git a/src/core/jpx.js b/src/core/jpx.js
index be0887a6d..a8206360c 100644
--- a/src/core/jpx.js
+++ b/src/core/jpx.js
@@ -736,7 +736,7 @@ var JpxImage = (function JpxImageClosure() {
     var l, r, c, p;
     var maxDecompositionLevelsCount = 0;
     for (c = 0; c < componentsCount; c++) {
-      var component = tile.components[c];
+      const component = tile.components[c];
       maxDecompositionLevelsCount = Math.max(
         maxDecompositionLevelsCount,
         component.codingStyleParameters.decompositionLevelsCount
@@ -768,7 +768,7 @@ var JpxImage = (function JpxImageClosure() {
       for (; r <= maxDecompositionLevelsCount; r++) {
         for (; p < maxNumPrecinctsInLevel[r]; p++) {
           for (; c < componentsCount; c++) {
-            var component = tile.components[c];
+            const component = tile.components[c];
             if (r > component.codingStyleParameters.decompositionLevelsCount) {
               continue;
             }
diff --git a/src/core/obj.js b/src/core/obj.js
index 931723f1c..b5ceccd61 100644
--- a/src/core/obj.js
+++ b/src/core/obj.js
@@ -894,12 +894,12 @@ class Catalog {
               break;
             }
             kidPromises.push(
-              xref.fetchAsync(kid).then(function(kid) {
-                if (!isDict(kid)) {
+              xref.fetchAsync(kid).then(function(obj) {
+                if (!isDict(obj)) {
                   throw new FormatError("Kid node must be a dictionary.");
                 }
-                if (kid.has("Count")) {
-                  total += kid.get("Count");
+                if (obj.has("Count")) {
+                  total += obj.get("Count");
                 } else {
                   // Page leaf node.
                   total++;
diff --git a/src/core/type1_parser.js b/src/core/type1_parser.js
index a8d4dd920..80428e4a8 100644
--- a/src/core/type1_parser.js
+++ b/src/core/type1_parser.js
@@ -612,7 +612,7 @@ var Type1Parser = (function Type1ParserClosure() {
             this.readInt(); // num
             this.getToken(); // read in 'array'
             while (this.getToken() === "dup") {
-              var index = this.readInt();
+              const index = this.readInt();
               length = this.readInt();
               this.getToken(); // read in 'RD' or '-|'
               data = length > 0 ? stream.getBytes(length) : new Uint8Array(0);
diff --git a/src/core/worker.js b/src/core/worker.js
index 1fee538f7..c92ac1958 100644
--- a/src/core/worker.js
+++ b/src/core/worker.js
@@ -182,19 +182,19 @@ var WorkerMessageHandler = {
 
     function getPdfManager(data, evaluatorOptions) {
       var pdfManagerCapability = createPromiseCapability();
-      var pdfManager;
+      let newPdfManager;
 
       var source = data.source;
       if (source.data) {
         try {
-          pdfManager = new LocalPdfManager(
+          newPdfManager = new LocalPdfManager(
             docId,
             source.data,
             source.password,
             evaluatorOptions,
             docBaseUrl
           );
-          pdfManagerCapability.resolve(pdfManager);
+          pdfManagerCapability.resolve(newPdfManager);
         } catch (ex) {
           pdfManagerCapability.reject(ex);
         }
@@ -220,7 +220,7 @@ var WorkerMessageHandler = {
           // We don't need auto-fetch when streaming is enabled.
           var disableAutoFetch =
             source.disableAutoFetch || fullRequest.isStreamingSupported;
-          pdfManager = new NetworkPdfManager(
+          newPdfManager = new NetworkPdfManager(
             docId,
             pdfStream,
             {
@@ -233,16 +233,15 @@ var WorkerMessageHandler = {
             evaluatorOptions,
             docBaseUrl
           );
-          // There may be a chance that `pdfManager` is not initialized
-          // for first few runs of `readchunk` block of code. Be sure
-          // to send all cached chunks, if any, to chunked_stream via
-          // pdf_manager.
+          // 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++) {
-            pdfManager.sendProgressiveData(cachedChunks[i]);
+            newPdfManager.sendProgressiveData(cachedChunks[i]);
           }
 
           cachedChunks = [];
-          pdfManagerCapability.resolve(pdfManager);
+          pdfManagerCapability.resolve(newPdfManager);
           cancelXHRs = null;
         })
         .catch(function(reason) {
@@ -258,33 +257,32 @@ var WorkerMessageHandler = {
         }
         // the data is array, instantiating directly from it
         try {
-          pdfManager = new LocalPdfManager(
+          newPdfManager = new LocalPdfManager(
             docId,
             pdfFile,
             source.password,
             evaluatorOptions,
             docBaseUrl
           );
-          pdfManagerCapability.resolve(pdfManager);
+          pdfManagerCapability.resolve(newPdfManager);
         } catch (ex) {
           pdfManagerCapability.reject(ex);
         }
         cachedChunks = [];
       };
       var readPromise = new Promise(function(resolve, reject) {
-        var readChunk = function(chunk) {
+        var readChunk = function({ value, done }) {
           try {
             ensureNotTerminated();
-            if (chunk.done) {
-              if (!pdfManager) {
+            if (done) {
+              if (!newPdfManager) {
                 flushChunks();
               }
               cancelXHRs = null;
               return;
             }
 
-            var data = chunk.value;
-            loaded += arrayByteLength(data);
+            loaded += arrayByteLength(value);
             if (!fullRequest.isStreamingSupported) {
               handler.send("DocProgress", {
                 loaded,
@@ -292,10 +290,10 @@ var WorkerMessageHandler = {
               });
             }
 
-            if (pdfManager) {
-              pdfManager.sendProgressiveData(data);
+            if (newPdfManager) {
+              newPdfManager.sendProgressiveData(value);
             } else {
-              cachedChunks.push(data);
+              cachedChunks.push(value);
             }
 
             fullRequest.read().then(readChunk, reject);
@@ -332,9 +330,9 @@ var WorkerMessageHandler = {
 
           handler
             .sendWithPromise("PasswordRequest", ex)
-            .then(function(data) {
+            .then(function({ password }) {
               finishWorkerTask(task);
-              pdfManager.updatePassword(data.password);
+              pdfManager.updatePassword(password);
               pdfManagerReady();
             })
             .catch(function() {