Question

Is there a difference between calling a javascript function with or without the new keyword? For instance if I had the function:

function computer(){
  this.hardDrive = "big";
  this.processor = "fast";
}

and I then call it in two different ways:

var hp = computer();
var hp = new computer();

what is going to be the difference between the two function calls?

Answer 1

Without new, this refers to the global object, and not any object returned from the function.

If you were to execute your code, you’d find that the first hp would be undefined, whereas the second would be [object Object]. Further, for obvious reasons, the first would not have a property of hardDrive or processor, but the second would.

In the first example, your two properties would have been added to the window object.