What do you understand by this keyword in JavaScript?

Answer 1

In JavaScript the this is a context-pointer and not an object pointer. It gives you the top-most context that is placed on the stack. The following gives two different results (in the browser, where by-default the window object is the 0-level context):

var obj = { outerWidth : 20 };

function say() {
    alert(this.outerWidth);
}

say();//will alert window.outerWidth
say.apply(obj);//will alert obj.outerWidth