From f6ec0d05351db89dbfc510148b3fdf4c89e647b5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Raphael=20von=20der=20Gr=C3=BCn?= <raphinesse@gmail.com>
Date: Thu, 18 Jul 2019 18:51:53 +0200
Subject: [PATCH] Run client-side JS through Babel if requested

---
 Gruntfile.js         | 29 +++++++++++++++++++++++------
 build-tools/build.js | 22 +++++++++++++++++++++-
 package.json         |  2 ++
 test/build.js        |  2 ++
 4 files changed, 48 insertions(+), 7 deletions(-)

diff --git a/Gruntfile.js b/Gruntfile.js
index 3f8ae47ff..7479e0402 100644
--- a/Gruntfile.js
+++ b/Gruntfile.js
@@ -25,12 +25,28 @@ module.exports = function (grunt) {
     grunt.initConfig({
         pkg: grunt.file.readJSON('package.json'),
         compile: {
-            'android': {},
-            'ios': {},
-            'osx': {},
-            'windows': { useWindowsLineEndings: true },
-            'browser': {},
-            'electron': {}
+            android: {
+                targets: 'Android >= 4.4, ChromeAndroid >= 30'
+            },
+            ios: {
+                targets: 'iOS >= 9'
+            },
+            osx: {
+                // TODO: add actual targets based on platform support
+                // {} means transform any ES2015+ code to ES5
+                targets: {}
+            },
+            windows: {
+                targets: 'Explorer >= 11',
+                useWindowsLineEndings: true
+            },
+            browser: {
+                // {} means transform any ES2015+ code to ES5
+                targets: {}
+            },
+            electron: {
+                targets: 'Electron >= 4'
+            }
         },
         clean: ['pkg']
     });
@@ -45,6 +61,7 @@ module.exports = function (grunt) {
 
         build({
             platformName: this.target,
+            babel: { targets: this.data.targets },
             platformVersion: grunt.option('platformVersion') ||
                              require(platformPkgPath).version,
             extraModules: collectModules(platformModulesPath)
diff --git a/build-tools/build.js b/build-tools/build.js
index 0b6fc8797..d3c44eb44 100644
--- a/build-tools/build.js
+++ b/build-tools/build.js
@@ -17,6 +17,7 @@
  * under the License.
  */
 
+const babel = require('@babel/core');
 const execa = require('execa');
 const bundle = require('./bundle');
 const scripts = require('./scripts');
@@ -34,9 +35,28 @@ module.exports = function build (userConfig) {
         .then(([ scripts, modules, commitId ]) => {
             Object.assign(config, { commitId });
             return bundle(scripts, modules, config);
-        });
+        })
+        .then(babelTransform(config));
 };
 
 function getCommitId () {
     return execa.stdout('git', ['rev-parse', 'HEAD'], { cwd: pkgRoot });
 }
+
+function babelTransform (config) {
+    const targets = (config.babel || {}).targets;
+    if (!targets) return x => x;
+
+    const babelOpts = {
+        retainLines: true,
+        presets: [
+            ['@babel/preset-env', {
+                targets,
+                // Do not force strict mode as that breaks some platforms
+                modules: false
+            }]
+        ]
+    };
+    return inputCode => babel.transformAsync(inputCode, babelOpts)
+        .then(result => result.code);
+}
diff --git a/package.json b/package.json
index 9dd7aa12d..4f6bd14ff 100644
--- a/package.json
+++ b/package.json
@@ -69,6 +69,8 @@
     }
   ],
   "dependencies": {
+    "@babel/core": "^7.6.4",
+    "@babel/preset-env": "^7.6.3",
     "execa": "^1.0.0",
     "fs-extra": "^8.0.1",
     "globby": "^9.2.0"
diff --git a/test/build.js b/test/build.js
index 5a54eb073..ba8bd0e56 100755
--- a/test/build.js
+++ b/test/build.js
@@ -25,6 +25,8 @@ function buildCordovaJsTestBundle (bundlePath) {
         platformName: 'test',
         platformVersion: 'N/A',
         extraModules: collectTestBuildModules(),
+        // {} means transform any ES2015+ code to ES5
+        babel: { targets: {} },
         preprocess (f) {
             // Do not instrument our test dummies
             if (f.path.includes('src/legacy-exec/test/')) return f;