[api-minor] Add the Babel targets-option to avoid transpiling code for unsupported browsers

Currently we simply use the Babel `preset-env` in the `legacy`-builds of the PDF.js library. This has the side-effect of transpiling the code for *very old* browsers/environments, including ones that we (since many years) no longer support which unnecessarily bloats the size of the `legacy`-builds.

For the CSS files we're only targeting *the supported browsers*, and it's thus possible to extend that to also apply to Babel.
One of the most significant changes, with this patch, is that we'll no longer polyfill `async`/`await` in the `legacy`-builds. However, this shouldn't be an issue given the browsers that we currently support in PDF.js; please refer to:
 - https://github.com/mozilla/pdf.js/wiki/Frequently-Asked-Questions#faq-support
 - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function#browser_compatibility

README.md

@@ -24,7 +24,7 @@ Feel free to stop by our [Matrix room](https://chat.mozilla.org/#/room/#pdfjs:mo
 ### Online demo
 
 Please note that the "Modern browsers" version assumes native support for
-features such as `async`/`await`, optional chaining, nullish coalescing,
+features such as optional chaining, nullish coalescing,
 and private `class` fields/methods.
 
 + Modern browsers: https://mozilla.github.io/pdf.js/web/viewer.html

external/dist/README.md

@@ -8,7 +8,7 @@ This is a pre-built version of the PDF.js source code. It is automatically
 generated by the build scripts.
 
 For usage with older browsers or environments, without support for modern
-features such as `async`/`await`, optional chaining, nullish coalescing,
+features such as optional chaining, nullish coalescing,
 and private `class` fields/methods; please see the `legacy/` folder.
 
 See https://github.com/mozilla/pdf.js for learning and contributing.

gulpfile.js

@@ -78,18 +78,22 @@ const builder = require("./external/builder/builder.js");
 const CONFIG_FILE = "pdfjs.config";
 const config = JSON.parse(fs.readFileSync(CONFIG_FILE).toString());
 
+const ENV_TARGETS = [
+  "last 2 versions",
+  "Chrome >= 76",
+  "Firefox ESR",
+  "Safari >= 13.1",
+  "> 1%",
+  "not IE > 0",
+  "not dead",
+];
+
 // Default Autoprefixer config used for generic, components, minified-pre
 const AUTOPREFIXER_CONFIG = {
-  overrideBrowserslist: [
+  overrideBrowserslist: ENV_TARGETS,
-    "last 2 versions",
-    "Chrome >= 76",
-    "Firefox ESR",
-    "Safari >= 13.1",
-    "> 1%",
-    "not IE > 0",
-    "not dead",
-  ],
 };
+// Default Babel targets used for generic, components, minified-pre
+const BABEL_TARGETS = ENV_TARGETS.join(", ");
 
 const DEFINES = Object.freeze({
   PRODUCTION: true,
@@ -213,16 +217,7 @@ function createWebpackConfig(
   }
   const babelExcludeRegExp = new RegExp(`(${babelExcludes.join("|")})`);
 
-  const babelPlugins = [
+  const babelPlugins = ["@babel/plugin-transform-modules-commonjs"];
-    "@babel/plugin-transform-modules-commonjs",
-    [
-      "@babel/plugin-transform-runtime",
-      {
-        helpers: false,
-        regenerator: true,
-      },
-    ],
-  ];
 
   const plugins = [];
   if (!disableLicenseHeader) {
@@ -262,6 +257,7 @@ function createWebpackConfig(
           options: {
             presets: skipBabel ? undefined : ["@babel/preset-env"],
             plugins: babelPlugins,
+            targets: BABEL_TARGETS,
           },
         },
         {
@@ -1493,15 +1489,9 @@ function buildLibHelper(bundleDefines, inputStream, outputDir) {
       presets: skipBabel ? undefined : ["@babel/preset-env"],
       plugins: [
         "@babel/plugin-transform-modules-commonjs",
-        [
-          "@babel/plugin-transform-runtime",
-          {
-            helpers: false,
-            regenerator: true,
-          },
-        ],
         babelPluginReplaceNonWebpackImports,
       ],
+      targets: BABEL_TARGETS,
     }).code;
     const removeCjsSrc =
       /^(var\s+\w+\s*=\s*(_interopRequireDefault\()?require\(".*?)(?:\/src)(\/[^"]*"\)\)?;)$/gm;

package-lock.json

@@ -10,7 +10,6 @@
       "devDependencies": {
         "@babel/core": "^7.18.10",
         "@babel/plugin-transform-modules-commonjs": "^7.18.6",
-        "@babel/plugin-transform-runtime": "^7.18.10",
         "@babel/preset-env": "^7.18.10",
         "@babel/runtime": "^7.18.9",
         "@javascript-obfuscator/escodegen": "2.3.0",
@@ -1502,35 +1501,6 @@
         "@babel/core": "^7.0.0-0"
       }
     },
-    "node_modules/@babel/plugin-transform-runtime": {
-      "version": "7.18.10",
-      "resolved": "https://registry.npmjs.org/@babel/plugin-transform-runtime/-/plugin-transform-runtime-7.18.10.tgz",
-      "integrity": "sha512-q5mMeYAdfEbpBAgzl7tBre/la3LeCxmDO1+wMXRdPWbcoMjR3GiXlCLk7JBZVVye0bqTGNMbt0yYVXX1B1jEWQ==",
-      "dev": true,
-      "dependencies": {
-        "@babel/helper-module-imports": "^7.18.6",
-        "@babel/helper-plugin-utils": "^7.18.9",
-        "babel-plugin-polyfill-corejs2": "^0.3.2",
-        "babel-plugin-polyfill-corejs3": "^0.5.3",
-        "babel-plugin-polyfill-regenerator": "^0.4.0",
-        "semver": "^6.3.0"
-      },
-      "engines": {
-        "node": ">=6.9.0"
-      },
-      "peerDependencies": {
-        "@babel/core": "^7.0.0-0"
-      }
-    },
-    "node_modules/@babel/plugin-transform-runtime/node_modules/semver": {
-      "version": "6.3.0",
-      "resolved": "https://registry.npmjs.org/semver/-/semver-6.3.0.tgz",
-      "integrity": "sha512-b39TBaTSfV6yBrapU89p5fKekE2m/NwnDocOVruQFS1/veMgdzuPcnOM34M6CwxW8jH/lxEa5rBoDeUwu5HHTw==",
-      "dev": true,
-      "bin": {
-        "semver": "bin/semver.js"
-      }
-    },
     "node_modules/@babel/plugin-transform-shorthand-properties": {
       "version": "7.18.6",
       "resolved": "https://registry.npmjs.org/@babel/plugin-transform-shorthand-properties/-/plugin-transform-shorthand-properties-7.18.6.tgz",
@@ -19877,28 +19847,6 @@
         "@babel/helper-plugin-utils": "^7.18.6"
       }
     },
-    "@babel/plugin-transform-runtime": {
-      "version": "7.18.10",
-      "resolved": "https://registry.npmjs.org/@babel/plugin-transform-runtime/-/plugin-transform-runtime-7.18.10.tgz",
-      "integrity": "sha512-q5mMeYAdfEbpBAgzl7tBre/la3LeCxmDO1+wMXRdPWbcoMjR3GiXlCLk7JBZVVye0bqTGNMbt0yYVXX1B1jEWQ==",
-      "dev": true,
-      "requires": {
-        "@babel/helper-module-imports": "^7.18.6",
-        "@babel/helper-plugin-utils": "^7.18.9",
-        "babel-plugin-polyfill-corejs2": "^0.3.2",
-        "babel-plugin-polyfill-corejs3": "^0.5.3",
-        "babel-plugin-polyfill-regenerator": "^0.4.0",
-        "semver": "^6.3.0"
-      },
-      "dependencies": {
-        "semver": {
-          "version": "6.3.0",
-          "resolved": "https://registry.npmjs.org/semver/-/semver-6.3.0.tgz",
-          "integrity": "sha512-b39TBaTSfV6yBrapU89p5fKekE2m/NwnDocOVruQFS1/veMgdzuPcnOM34M6CwxW8jH/lxEa5rBoDeUwu5HHTw==",
-          "dev": true
-        }
-      }
-    },
     "@babel/plugin-transform-shorthand-properties": {
       "version": "7.18.6",
       "resolved": "https://registry.npmjs.org/@babel/plugin-transform-shorthand-properties/-/plugin-transform-shorthand-properties-7.18.6.tgz",

package.json

@@ -3,7 +3,6 @@
   "devDependencies": {
     "@babel/core": "^7.18.10",
     "@babel/plugin-transform-modules-commonjs": "^7.18.6",
-    "@babel/plugin-transform-runtime": "^7.18.10",
     "@babel/preset-env": "^7.18.10",
     "@babel/runtime": "^7.18.9",
     "@javascript-obfuscator/escodegen": "2.3.0",