title: Angular2 & Typescript - Property name does not exist on type
body: <p>The suggested answer to <a href="https://stackoverflow.com/questions/44095483/angular2-typescript-how-to-retrieve-an-array-from-inside-an-object">this question</a> using find does not work in Typescript, it cannot compile. I've looked at other similar questions, but they all seem a little different (context) in some way.</p>
  
  <p>This is the array:</p>
  
  <pre><code>categories: Category[] = [];
  </code></pre>
  
  <p>This is Category object:</p>
  
  <pre><code>export class Category{
    constructor(
      id: string,
      name: string,
      category_types: Object[]
    ) {}
  }
  </code></pre>
  
  <p>and I am trying to find like this (value is a string, eg 'Wood'):</p>
  
  <pre><code>let a = this.categories.find(v =&gt; v.name === value);
  </code></pre>
  
  <p>It says Property name does not exist on type 'Category'.</p>