when we try to call document object methods with direct refrence ex: var kk = document.getElementById; kk("someid") gives error?

Question

var kk = document.getElementById;
kk("some_id");  // gives Uncaught TypeError: Illegal invocation in chrome

but if we do that same with user defined object it works.

var obj = {
    some_function : function(a){
        alert(a);
    }
};
var kk = obj.some_function;
kk("hello");  // works

what is the reason for this error. i just checked in google chrome and it is not working, i came across this when i was creating a short version for document.getElementById, by var $id = document.getElementById; but it did not work. and one interesting thing is that here $id === document.getElementById; (true) and typeof $id is function.

is that because of some security reasons or something ? sorry for weak english and i m not even good at making good title for questions. thanks for answers.

Answer 1

Use Function.prototype.bind(). It will bind context to document.

var kk = document.getElementById.bind(document);