title: Assign value to `readonly` properties from methods called by the constructor
body: <p>I have a simple class, and I want to assign a value to a readonly property in a method initiated by the constructor, but it says <code>[ts] Cannot assign to 'readOnlyProperty' because it is a constant or a read-only property.</code>
  Why can't I assign a value to the property even though I am calling <code>process</code> from the constructor?</p>
  
  <p>Sample Code:</p>
  
  <pre><code>class C {
      readonly readOnlyProperty: string;
      constructor(raw: string) {
          this.process(raw);
      }
      process(raw: string) {
          this.readOnlyProperty = raw; // [ts] Cannot assign to 'readOnlyProperty' because it is a constant or a read-only property.
      }
  }
  </code></pre>