title: Typescript custom interface variable declaration
body: <p>TypeScript novice here, and i'm currently learning the language on <a href="https://www.tutorialspoint.com/typescript/typescript_interfaces.htm" rel="nofollow noreferrer">TutorialsPoint here</a>.
  I'm currently having a hard time understanding the differences between these two pieces of code.</p>
  
  <pre><code>interface Person{
      age: number;
  }
  
  interface Musician extends Person{
      instrument: string;
  }
  
  var drummer:Musician = {
      instrument: "drum",
      age: 28
  }
  </code></pre>
  
  <p>and</p>
  
  <pre><code>interface Person{
      age: number;
  }
  
  interface Musician extends Person{
      instrument: string;
  }
  
  var drummer = &lt;Musician&gt;{}
  drummer.instrument = "drum"
  drummer.age = 28
  </code></pre>
  
  <p>What is the difference between the two? and is there a specific situation where it is better to use the first/second implementation?</p>
  
  <p>Thank you.</p>