diff --git a/.eslintignore b/.eslintignore
index d149d0f58..e72c6d82f 100644
--- a/.eslintignore
+++ b/.eslintignore
@@ -4,7 +4,6 @@ docs/
 node_modules/
 external/bcmaps/
 external/webL10n/
-external/cmapscompress/
 external/builder/fixtures/
 external/builder/fixtures_esprima/
 external/quickjs/
diff --git a/external/cmapscompress/.eslintrc b/external/cmapscompress/.eslintrc
new file mode 100644
index 000000000..4a0b538f6
--- /dev/null
+++ b/external/cmapscompress/.eslintrc
@@ -0,0 +1,10 @@
+{
+  "extends": [
+    "../.eslintrc"
+  ],
+
+  "rules": {
+    // ECMAScript 6
+    "no-var": "error",
+  },
+}
diff --git a/external/cmapscompress/compress.js b/external/cmapscompress/compress.js
index 684fe5184..2367a061f 100644
--- a/external/cmapscompress/compress.js
+++ b/external/cmapscompress/compress.js
@@ -37,7 +37,7 @@ function compressCmap(srcPath, destPath, verify) {
     const first = item.items[0];
     const sequence = item.sequence === true;
     const flags = (item.type << 5) | (sequence ? 0x10 : 0);
-    var nextStart, nextCode;
+    let nextStart, nextCode;
     switch (item.type) {
       case 0:
         out +=
@@ -45,7 +45,7 @@ function compressCmap(srcPath, destPath, verify) {
           writeNumber(subitems.length);
         out += first.start + writeNumber(subHex(first.end, first.start));
         nextStart = incHex(first.end);
-        for (var j = 1; j < subitems.length; j++) {
+        for (let j = 1; j < subitems.length; j++) {
           out +=
             writeNumber(subHex(subitems[j].start, nextStart)) +
             writeNumber(subHex(subitems[j].end, subitems[j].start));
@@ -61,7 +61,7 @@ function compressCmap(srcPath, destPath, verify) {
           writeNumber(subHex(first.end, first.start)) +
           writeNumber(first.code);
         nextStart = incHex(first.end);
-        for (var j = 1; j < subitems.length; j++) {
+        for (let j = 1; j < subitems.length; j++) {
           out +=
             writeNumber(subHex(subitems[j].start, nextStart)) +
             writeNumber(subHex(subitems[j].end, subitems[j].start)) +
@@ -76,7 +76,7 @@ function compressCmap(srcPath, destPath, verify) {
         out += first.char + writeNumber(first.code);
         nextStart = incHex(first.char);
         nextCode = first.code + 1;
-        for (var j = 1; j < subitems.length; j++) {
+        for (let j = 1; j < subitems.length; j++) {
           out +=
             (sequence ? "" : writeNumber(subHex(subitems[j].char, nextStart))) +
             writeSigned(subitems[j].code - nextCode);
@@ -93,7 +93,7 @@ function compressCmap(srcPath, destPath, verify) {
           writeNumber(subHex(first.end, first.start)) +
           writeNumber(first.code);
         nextStart = incHex(first.end);
-        for (var j = 1; j < subitems.length; j++) {
+        for (let j = 1; j < subitems.length; j++) {
           out +=
             (sequence
               ? ""
@@ -110,7 +110,7 @@ function compressCmap(srcPath, destPath, verify) {
         out += first.char + first.code;
         nextStart = incHex(first.char);
         nextCode = incHex(first.code);
-        for (var j = 1; j < subitems.length; j++) {
+        for (let j = 1; j < subitems.length; j++) {
           out +=
             (sequence ? "" : writeNumber(subHex(subitems[j].char, nextStart))) +
             writeSigned(subHex(subitems[j].code, nextCode));
@@ -127,7 +127,7 @@ function compressCmap(srcPath, destPath, verify) {
           writeNumber(subHex(first.end, first.start)) +
           first.code;
         nextStart = incHex(first.end);
-        for (var j = 1; j < subitems.length; j++) {
+        for (let j = 1; j < subitems.length; j++) {
           out +=
             (sequence
               ? ""
@@ -140,11 +140,11 @@ function compressCmap(srcPath, destPath, verify) {
     }
   }
 
-  fs.writeFileSync(destPath, new Buffer(out, "hex"));
+  fs.writeFileSync(destPath, Buffer.from(out, "hex"));
 
   if (verify) {
     const result2 = parseCMap(out);
-    const isGood = JSON.stringify(inputData) == JSON.stringify(result2);
+    const isGood = JSON.stringify(inputData) === JSON.stringify(result2);
     if (!isGood) {
       throw new Error("Extracted data does not match the expected result");
     }
@@ -191,8 +191,9 @@ function parseCMap(binaryData) {
       return s;
     },
     readHexNumber(size) {
-      const lengthInChars = (size + 1) << 1;
-      const stack = [];
+      const lengthInChars = (size + 1) << 1,
+        stack = [];
+      let last;
       do {
         const b = this.readByte();
         last = !(b & 0x80);
@@ -269,13 +270,13 @@ function parseCMap(binaryData) {
     }
     const ucs2DataSize = 1;
     const subitemsCount = reader.readNumber();
-    var start, end, code, char;
+    let start, end, code, char;
     switch (type) {
       case 0:
         start = reader.readHex(dataSize);
         end = addHex(reader.readHexNumber(dataSize), start);
         subitems.push({ start, end });
-        for (var i = 1; i < subitemsCount; i++) {
+        for (let i = 1; i < subitemsCount; i++) {
           start = addHex(reader.readHexNumber(dataSize), incHex(end));
           end = addHex(reader.readHexNumber(dataSize), start);
           subitems.push({ start, end });
@@ -286,7 +287,7 @@ function parseCMap(binaryData) {
         end = addHex(reader.readHexNumber(dataSize), start);
         code = reader.readNumber();
         subitems.push({ start, end, code });
-        for (var i = 1; i < subitemsCount; i++) {
+        for (let i = 1; i < subitemsCount; i++) {
           start = addHex(reader.readHexNumber(dataSize), incHex(end));
           end = addHex(reader.readHexNumber(dataSize), start);
           code = reader.readNumber();
@@ -297,7 +298,7 @@ function parseCMap(binaryData) {
         char = reader.readHex(dataSize);
         code = reader.readNumber();
         subitems.push({ char, code });
-        for (var i = 1; i < subitemsCount; i++) {
+        for (let i = 1; i < subitemsCount; i++) {
           char = sequence
             ? incHex(char)
             : addHex(reader.readHexNumber(dataSize), incHex(char));
@@ -310,7 +311,7 @@ function parseCMap(binaryData) {
         end = addHex(reader.readHexNumber(dataSize), start);
         code = reader.readNumber();
         subitems.push({ start, end, code });
-        for (var i = 1; i < subitemsCount; i++) {
+        for (let i = 1; i < subitemsCount; i++) {
           start = sequence
             ? incHex(end)
             : addHex(reader.readHexNumber(dataSize), incHex(end));
@@ -323,7 +324,7 @@ function parseCMap(binaryData) {
         char = reader.readHex(ucs2DataSize);
         code = reader.readHex(dataSize);
         subitems.push({ char, code });
-        for (var i = 1; i < subitemsCount; i++) {
+        for (let i = 1; i < subitemsCount; i++) {
           char = sequence
             ? incHex(char)
             : addHex(reader.readHexNumber(ucs2DataSize), incHex(char));
@@ -336,7 +337,7 @@ function parseCMap(binaryData) {
         end = addHex(reader.readHexNumber(ucs2DataSize), start);
         code = reader.readHex(dataSize);
         subitems.push({ start, end, code });
-        for (var i = 1; i < subitemsCount; i++) {
+        for (let i = 1; i < subitemsCount; i++) {
           start = sequence
             ? incHex(end)
             : addHex(reader.readHexNumber(ucs2DataSize), incHex(end));
@@ -368,7 +369,7 @@ function writeByte(b) {
 }
 function writeNumber(n) {
   if (typeof n === "string") {
-    var s = "",
+    let s = "",
       buffer = 0,
       bufferSize = 0;
     let i = n.length;
@@ -390,7 +391,7 @@ function writeNumber(n) {
     }
     return s;
   }
-  var s = writeByte(n & 0x7f);
+  let s = writeByte(n & 0x7f);
   n >>>= 7;
   while (n > 0) {
     s = writeByte((n & 0x7f) | 0x80) + s;
@@ -470,7 +471,7 @@ function incHex(a) {
 
 exports.compressCmaps = function (src, dest, verify) {
   const files = fs.readdirSync(src).filter(function (fn) {
-    return fn.indexOf(".") < 0; // skipping files with the extension
+    return !fn.includes("."); // skipping files with the extension
   });
   files.forEach(function (fn) {
     const srcPath = path.join(src, fn);
diff --git a/external/cmapscompress/optimize.js b/external/cmapscompress/optimize.js
index 86e722094..231912bb5 100644
--- a/external/cmapscompress/optimize.js
+++ b/external/cmapscompress/optimize.js
@@ -14,7 +14,7 @@
  */
 
 exports.optimizeCMap = function (data) {
-  var i = 1;
+  let i = 1;
   while (i < data.body.length) {
     if (data.body[i - 1].type === data.body[i].type) {
       data.body[i - 1].items = data.body[i - 1].items.concat(
@@ -26,16 +26,16 @@ exports.optimizeCMap = function (data) {
     }
   }
   // split into groups with different lengths
-  var i = 0;
+  i = 0;
   while (i < data.body.length) {
-    var item = data.body[i];
-    const keys = Object.keys(item.items[0]).filter(function (i) {
-      return typeof item.items[0][i] === "string";
+    const item = data.body[i];
+    const keys = Object.keys(item.items[0]).filter(function (val) {
+      return typeof item.items[0][val] === "string";
     });
-    var j = 1;
+    let j = 1;
     while (j < item.items.length) {
       let different = false;
-      for (var q = 0; q < keys.length && !different; q++) {
+      for (let q = 0; q < keys.length && !different; q++) {
         different =
           item.items[j - 1][keys[q]].length !== item.items[j][keys[q]].length;
       }
@@ -53,13 +53,13 @@ exports.optimizeCMap = function (data) {
     i++;
   }
   // find sequences of single char ranges
-  var i = 0;
+  i = 0;
   while (i < data.body.length) {
-    var item = data.body[i];
+    const item = data.body[i];
     if (item.type === 3 || item.type === 5) {
-      var j = 0;
+      let j = 0;
       while (j < item.items.length) {
-        var q = j;
+        const q = j;
         while (
           j < item.items.length &&
           item.items[j].start === item.items[j].end
@@ -76,15 +76,15 @@ exports.optimizeCMap = function (data) {
           if (q > 0) {
             data.body.splice(i + 1, 0, {
               type: item.type - 1,
-              items: item.items.splice(q, j - q).map(function (i) {
-                return { char: i.start, code: i.code };
+              items: item.items.splice(q, j - q).map(function (val) {
+                return { char: val.start, code: val.code };
               }),
             });
             i++;
           } else {
             item.type -= 1;
-            item.items = item.items.map(function (i) {
-              return { char: i.start, code: i.code };
+            item.items = item.items.map(function (val) {
+              return { char: val.start, code: val.code };
             });
           }
           continue;
@@ -95,16 +95,16 @@ exports.optimizeCMap = function (data) {
     i++;
   }
 
-  //  find sequences of increasing code/ranges order
-  var i = 0;
+  // find sequences of increasing code/ranges order
+  i = 0;
   while (i < data.body.length) {
-    var item = data.body[i];
+    const item = data.body[i];
     if (item.type >= 2 && item.type <= 5) {
-      var j = 1;
+      let j = 1;
       const startProp = item.type === 2 || item.type === 4 ? "char" : "start";
       const endProp = item.type === 2 || item.type === 4 ? "char" : "end";
       while (j < item.items.length) {
-        var q = j - 1;
+        const q = j - 1;
         while (
           j < item.items.length &&
           incHex(item.items[j - 1][endProp]) === item.items[j][startProp]
@@ -137,18 +137,18 @@ exports.optimizeCMap = function (data) {
   }
 
   // split non-sequences two groups where codes are close
-  var i = 0;
+  i = 0;
   while (i < data.body.length) {
-    var item = data.body[i];
+    const item = data.body[i];
     if (!item.sequence && (item.type === 2 || item.type === 3)) {
       const subitems = item.items;
-      const codes = subitems.map(function (i) {
-        return i.code;
+      const codes = subitems.map(function (val) {
+        return val.code;
       });
       codes.sort(function (a, b) {
         return a - b;
       });
-      var maxDistance = 100,
+      const maxDistance = 100,
         minItems = 10,
         itemsPerBucket = 50;
       if (
@@ -157,12 +157,12 @@ exports.optimizeCMap = function (data) {
       ) {
         const gapsCount = Math.max(2, (subitems.length / itemsPerBucket) | 0);
         const gaps = [];
-        for (var q = 0; q < gapsCount; q++) {
+        for (let q = 0; q < gapsCount; q++) {
           gaps.push({ length: 0 });
         }
-        for (var j = 1; j < codes.length; j++) {
+        for (let j = 1; j < codes.length; j++) {
           const gapLength = codes[j] - codes[j - 1];
-          var q = 0;
+          let q = 0;
           while (q < gaps.length && gaps[q].length > gapLength) {
             q++;
           }
@@ -190,15 +190,15 @@ exports.optimizeCMap = function (data) {
         });
         if (groups.length > 1) {
           const buckets = [(item.items = [])];
-          for (var j = 0; j < groups.length; j++) {
+          for (let j = 0; j < groups.length; j++) {
             const newItem = { type: item.type, items: [] };
             buckets.push(newItem.items);
             i++;
             data.body.splice(i, 0, newItem);
           }
-          for (var j = 0; j < subitems.length; j++) {
+          for (let j = 0; j < subitems.length; j++) {
             const code = subitems[j].code;
-            var q = 0;
+            let q = 0;
             while (q < groups.length && groups[q] <= code) {
               q++;
             }
diff --git a/external/cmapscompress/parse.js b/external/cmapscompress/parse.js
index 374c530c1..1565eaa17 100644
--- a/external/cmapscompress/parse.js
+++ b/external/cmapscompress/parse.js
@@ -32,21 +32,21 @@ exports.parseAdobeCMap = function (content) {
   result.type = +m[1];
   m = /\/WMode\s+(\d+)+\s+def\b/.exec(body);
   result.wmode = +m[1];
-  m = /\/([\w\-]+)\s+usecmap\b/.exec(body);
+  m = /\/([\w-]+)\s+usecmap\b/.exec(body);
   if (m) {
     result.usecmap = m[1];
   }
   const re = /(\d+)\s+(begincodespacerange|beginnotdefrange|begincidchar|begincidrange|beginbfchar|beginbfrange)\n([\s\S]*?)\n(endcodespacerange|endnotdefrange|endcidchar|endcidrange|endbfchar|endbfrange)/g;
   while ((m = re.exec(body))) {
     const lines = m[3].toLowerCase().split("\n");
-    var m2;
+
     switch (m[2]) {
       case "begincodespacerange":
         result.body.push({
           type: 0,
           items: lines.map(function (line) {
-            const m = /<(\w+)>\s+<(\w+)>/.exec(line);
-            return { start: m[1], end: m[2] };
+            const m2 = /<(\w+)>\s+<(\w+)>/.exec(line);
+            return { start: m2[1], end: m2[2] };
           }),
         });
         break;
@@ -54,8 +54,8 @@ exports.parseAdobeCMap = function (content) {
         result.body.push({
           type: 1,
           items: lines.map(function (line) {
-            const m = /<(\w+)>\s+<(\w+)>\s+(\d+)/.exec(line);
-            return { start: m[1], end: m[2], code: +m[3] };
+            const m2 = /<(\w+)>\s+<(\w+)>\s+(\d+)/.exec(line);
+            return { start: m2[1], end: m2[2], code: +m2[3] };
           }),
         });
         break;
@@ -63,8 +63,8 @@ exports.parseAdobeCMap = function (content) {
         result.body.push({
           type: 2,
           items: lines.map(function (line) {
-            const m = /<(\w+)>\s+(\d+)/.exec(line);
-            return { char: m[1], code: +m[2] };
+            const m2 = /<(\w+)>\s+(\d+)/.exec(line);
+            return { char: m2[1], code: +m2[2] };
           }),
         });
         break;
@@ -72,8 +72,8 @@ exports.parseAdobeCMap = function (content) {
         result.body.push({
           type: 3,
           items: lines.map(function (line) {
-            const m = /<(\w+)>\s+<(\w+)>\s+(\d+)/.exec(line);
-            return { start: m[1], end: m[2], code: +m[3] };
+            const m2 = /<(\w+)>\s+<(\w+)>\s+(\d+)/.exec(line);
+            return { start: m2[1], end: m2[2], code: +m2[3] };
           }),
         });
         break;
@@ -81,8 +81,8 @@ exports.parseAdobeCMap = function (content) {
         result.body.push({
           type: 4,
           items: lines.map(function (line) {
-            const m = /<(\w+)>\s+<(\w+)>/.exec(line);
-            return { char: m[1], code: m[2] };
+            const m2 = /<(\w+)>\s+<(\w+)>/.exec(line);
+            return { char: m2[1], code: m2[2] };
           }),
         });
         break;
@@ -90,8 +90,8 @@ exports.parseAdobeCMap = function (content) {
         result.body.push({
           type: 5,
           items: lines.map(function (line) {
-            const m = /<(\w+)>\s+<(\w+)>\s+<(\w+)>/.exec(line);
-            return { start: m[1], end: m[2], code: m[3] };
+            const m2 = /<(\w+)>\s+<(\w+)>\s+<(\w+)>/.exec(line);
+            return { start: m2[1], end: m2[2], code: m2[3] };
           }),
         });
         break;