> For the complete documentation index, see [llms.txt](https://huang-jason.gitbook.io/js-syntax/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://huang-jason.gitbook.io/js-syntax/this.md).

# this

```javascript
Game.prototype.restart = function () {
  this.clearLocalStorage();
  this.timer = setTimeout(function() {
    this.clearBoard();    // what is "this"?
  }, 0);
};
```

**error:** Uncaught TypeError: undefined is not a function

When you invoke `setTimeout()`, you are actually invoking `window.setTimeout()`. Therefore, `this.clearBoard();` refers to the **window** object.

## Traditional solution

* use `var self = this;`

```javascript
Game.prototype.restart = function () {
  this.clearLocalStorage();
  var self = this;   // save reference to 'this', while it's still this!
  this.timer = setTimeout(function(){
    self.clearBoard();    // oh OK, I do know who 'self' is!
  }, 0);
};
```

## New solution

* use the `bind()` method to pass in the proper reference:

```javascript
Game.prototype.restart = function () {
  this.clearLocalStorage();
  this.timer = setTimeout(this.reset.bind(this), 0);  // bind to 'this'
};

Game.prototype.reset = function(){
    this.clearBoard();    // ahhh, back in the context of the right 'this'!
};
```


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