Typescript “this” inside a class method

Question

I know this is probably painfully basic, but i am having a tough time wrapping my head around it.

class Main
{
     constructor()
     {
         requestAni         


        

Answer 1

See page 72 of the typescript language specification https://github.com/Microsoft/TypeScript/blob/master/doc/TypeScript%20Language%20Specification.pdf?raw=true

Arrow Function Expressions

In the example

class Messenger {
 message = "Hello World";
 start() {
 setTimeout(() => alert(this.message), 3000);
 }
};
var messenger = new Messenger();
messenger.start();

the use of an arrow function expression causes the callback to have the same this as the surrounding ‘start’ method. Writing the callback as a standard function expression it becomes necessary to manually arrange access to the surrounding this, for example by copying it into a local variable:

This is the actual generated Javascript:

class Messenger {
 message = "Hello World";
 start() {
 var _this = this;
 setTimeout(function() { alert(_this.message); }, 3000);
 }
};