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

The problem arises when you pass a function as a callback. By the time the callback has executed the value of "this" could have changed to the Window, the control invoking the callback, or something else.

Make sure you always use a lambda expression at the point you pass a reference to the function to be called back. For example

public addFile(file) {
  this.files.push(file);
}
//Not like this
someObject.doSomething(addFile);
//but instead, like this
someObject.doSomething( (file) => addFile(file) );

This compiles to something like

this.addFile(file) {
  this.files.push(file);
}
var _this = this;
someObject.doSomething(_this.addFile);

Because the addFile function is being called on a specific object reference (_this) it does not use the "this" of the invoker but instead the value of _this.