title: Object assign with inheritance not working in typescript
body: <p>The code was working when i was using it inside Angular project, then I decided to move to React and the code is working incorrectly.</p>
  
  <pre><code>class A {
    constructor(...parts: Partial&lt;A&gt;[]) {
      Object.assign(this, ...parts);
    }
  }
  
  class B extends A {
    id: string;
    constructor(...parts: Partial&lt;B&gt;[]) {
      super(...parts);
  
    }
  }
  
  const a = new B({ id: '123' });
  console.log(a);
  </code></pre>
  
  <p>The output of console log is <code>B {id: undefined}</code> and i expect it to be <code>B {id: '123'}</code></p>
  
  <p>Here is tsconfig:</p>
  
  <pre><code>{
    "compilerOptions": {
      "target": "es5",
      "lib": [
        "dom",
        "dom.iterable",
        "esnext"
      ],
      "allowJs": true,
      "skipLibCheck": true,
      "esModuleInterop": false,
      "allowSyntheticDefaultImports": true,
      "forceConsistentCasingInFileNames": true,
      "experimentalDecorators": true,
      "emitDecoratorMetadata": true,
      "module": "esnext",
      "moduleResolution": "node",
      "resolveJsonModule": true,
      "isolatedModules": true,
      "noEmit": true,
      "jsx": "preserve",
      "strict": false
    },
    "include": [
      "src"
    ]
  }
  </code></pre>
  
  <p>Here is the versions:</p>
  
  <pre><code>+ @types/jest@24.0.9
  + react-scripts@2.1.5
  + @types/react-dom@16.8.2
  + react@16.8.3
  + @types/react@16.8.6
  + typescript@3.3.3333
  + react-dom@16.8.3
  + @types/node@11.10.4
  + create-react-app@2.1.5
  </code></pre>
  
  <p>Minimum steps to reproduce:</p>
  
  <ul>
  <li>create-react-app test --typescript</li>
  <li>add code to App.tsx</li>
  <li>run and look into console</li>
  </ul>
  
  <p>UPDATED:</p>
  
  <p>I ended up using the following solution:</p>
  
  <pre><code>class B extends A {
    id: string = this.id;
  </code></pre>