title: What is dom for in the lib array in the tsconfig.json file in Angular?
body: <p>In my Angular 6 project, in tsconfig.json and ts.config.spec.json I have this part:</p>
  
  <pre><code>"lib": [
        "es2016",
        "dom"
      ]
  </code></pre>
  
  <p>What is <code>dom</code> for? </p>
  
  <p>Official documentation <a href="https://github.com/Microsoft/TypeScript/wiki/What&#39;s-new-in-TypeScript#including-built-in-type-declarations-with---lib" rel="noreferrer">here</a> says: "... you can exclude declarations you do not want to include in your project, e.g. DOM if you are working on a node project using --lib es5,es6."</p>
  
  <p>But I am not sure what this means in practice. We do not specify "any declarations you do not want." </p>
  
  <p>My tests were totally broken until I added <code>dom</code> to the <code>lib</code> array in tsconfig.spec.ts. What does this do?</p>