difference between functionName() and functionName.call() in javascript

Question

Hopefully the title is self explanatory, what is the advantage of using the .call() method in Javascript compared with just writing functionName(); ?

Answer 1

functionName.call() takes an object instance as its first parameter. It then runs functionName within the context of that object instance (ie "this" is the specified instance)

Answer 2

If you don't pass anything into call(), it will be the same; the function will be run with the same scope that the call to call() is made:

function test() {
    alert(this);
}

test(); // alerts the window object
test.call(); // alerts the window object

But if you pass an object into call(), that object will be used as the scope:

test.call("hi"); // alerts "hi"