"This" in Typescript class instance

Question

In javascript I could use either saving this to function-scoped _this, or binding function to this directly (Function.bind or underscorejs bind utilites).

But typescript is supposed to more object-oriented, and I was expecting this in typescript to point to the class instance. But it does work just as in JS. So I have to use construction

    export class Mouse {
        private board : Presentation.View.Board;
        private focus : Presentation.View.Element = null;
        constructor(board:Presentation.View.Board){
            var _this = this;
            board.bindMouse(
                function(event:JQueryEventObject){
                    if( _this.focus ) _this.focus.move(event);
                }
            );
        }

or

    export class Mouse {
        private board : Presentation.View.Board;
        private focus : Presentation.View.Element = null;
        constructor(board:Presentation.View.Board){
            var _this = this;
            board.bindMouse(
                _.bind(function(event:JQueryEventObject){
                    if( this.focus ) this.focus.move(event);
                }, this);
            );
        }

So I ask, are there any ways to avoid direct this micromanagement? I suppose there is a way to make some kind of augumentations so class instance always have some reference to inself (it can have any name, like that).

krlm · Accepted Answer · 2014-04-02 09:53:43Z

1

Use the arrow functions. Form the spec:

A function expression using the function keyword introduces a new dynamically bound this, whereas an arrow function expression preserves the this of its enclosing context. Arrow function expressions are particularly useful for writing callbacks, which otherwise often
have an undefined or unexpected this.

 board.bindMouse((event: JQueryEventObject) => {
       if(this.focus) this.focus.move(event);
 });

edited Apr 2, 2014 at 9:53

answered Mar 12, 2014 at 10:05

krlm

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2 Comments

setec Over a year ago

I really dislike this C-type syntax, but looks like its only good option.

Stephen Chung Over a year ago

That is strange, as I understand most developers like the arrow syntax.

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