title: Upgrade to Angular 8: Changing the target to "es2015" in tsconfig.json leads to error in polyfills-2015
body: <p>When changing the target to <strong>es2015</strong> (instead of es5), I get the following error when starting my app:</p>
  
  <pre><code>polyfills-es2015.4a168e5d0734802f67ed.js:1 Uncaught TypeError: Cannot set property 'true' of undefined
      at Object.6dTf (polyfills-es2015.4a168e5d0734802f67ed.js:1)
      at u (runtime-es2015.05393c8efcd0eb158773.js:1)
      at Module.hN/g (polyfills-es2015.4a168e5d0734802f67ed.js:1)
      at u (runtime-es2015.05393c8efcd0eb158773.js:1)
      at Object.1 (polyfills-es2015.4a168e5d0734802f67ed.js:1)
      at u (runtime-es2015.05393c8efcd0eb158773.js:1)
      at t (runtime-es2015.05393c8efcd0eb158773.js:1)
      at Array.r [as push] (runtime-es2015.05393c8efcd0eb158773.js:1)
      at polyfills-es2015.4a168e5d0734802f67ed.js:1
  </code></pre>
  
  <p>Also, I needed to <strong>import Zone.js in my main.ts</strong> file instead of polyfills.ts, otherwise I would get the error:</p>
  
  <blockquote>
    <p>in this configuration angular requires zone.js</p>
  </blockquote>
  
  <p>I am using Angular8, Typescript 3.4.5 and node 12.4.0. What am I doing wrong?</p>
  
  <p>My <strong>tsconfig.json:</strong></p>
  
  <pre><code>{
    "angularCompilerOptions": {
      "preserveWhitespaces": false
    },
    "compileOnSave": false,
    "exclude": [
      "test.ts",
      "**/*.spec.ts"
    ],
    "compilerOptions": {
      "outDir": "./dist/out-tsc/app",
      "sourceMap": true,
      "declaration": false,
      "moduleResolution": "node",
      "emitDecoratorMetadata": true,
      "experimentalDecorators": true,
      "target": "es6",
      "module": "esnext",
      "typeRoots": [
        "node_modules/@types"
      ],
      "lib": [
        "es6",
        "dom"
      ],
      "baseUrl": "./src"
    }
  }
  </code></pre>