Return this type instead of Matrix4 for in-place mutations

[TimJentzsch]

Objective

I would like to create a subclass of Matrix4 to add my own custom methods while maintaining type safety.
However, when using functions like .multiply, the subclass is "lost", because it returns type Matrix4.
In reality, .multiply is an in-place operation which returns this, so the subclass is preserved.

Example

export class Matrix4Ext extends Matrix4 {
  extension(): this {
    // -- Do stuff --
    return this;
  }
}

new Matrix4Ext()
  .multiply(new Matrix4())
  // Error: Property 'extension' does not exist on type 'Matrix4'.
  .extension();

Solution

The type definitions should be adjusted to return this instead of Matrix4 if the operation is in-place and this is returned.
Which type definitions have to be adjusted can be inferred from the Three.js documentation on Matrix4 (using the this type).

[Methuselah96]

Sure thing! Feel free to create a PR for this.