title: Create object with part of interface. Typescript
body: <p>I have a problem, please help.</p>
  
  <p>We have two interfaces:</p>
  
  <pre><code>interface IUserEntity {
      Id: number;
      FirstName: string;
      LastName: string;
  }
  
  interface IUserEntityMethods {
      GetFullName(): string;
  }
  </code></pre>
  
  <p>I would like to create an object that will have type <code>IUserEntityMethods</code>, but within the method <code>GetFullName</code> through <code>this</code> in Webstorm (for example) dropped autocomplete with the ability to use the properties of the interface <code>IUserEntity</code>.</p>
  
  <p>What I want to get in the end:</p>
  
  <pre><code>var userEntityMethods: IUserEntityMethods = {
      GetFullName: function() {
          return this.FirstName + " " + this.LastName; // We have no errors at this line.
      }
  }
  </code></pre>
  
  <p>Is this possible? Or is there any other option?</p>