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Incorrect Scope in JavaScript Function Invocation

When using the function invocation pattern (e.g. myFunc()) in JavaScript, the this variable is incorrectly bound to the global object. Ex.

var val = 2;
var obj = {
  val : 0,
  method : function(){
    function times(x){
      return this.val * x;
    }
    return times(5); // 10
  }
}
console.log(obj.method());

In the above example we would expect this.val to reference obj.val and therefore return 0. But instead this.val references window.val, and thus returns 10.

A work around for this incorrect scope in JavaScript is to create a new variable to store the higher order function's context. Below we use a variable named that to hold the scope of the outer function and then use that.val, which will reference obj.val.

var val = 2;
var obj = {
  val : 0,
  method : function(){
    var that = this; // 
    function times(x){
      return that.val * x;
    }
    return times(5); // 0
  }
}
console.log(obj.method());

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