Difference between function with a name and function without name in Javascript

Question

1.

function abc(){
    alert("named function");
}

v/s

2.

function(){
    alert("Un-Named function");
}

Kindly explain from beginners point.

Answer 1

They work exactly the same. It's only in how you are able to run them that they are different.

So example #1 you could call again at any point with abc();. For example 2, you would either have to pass it as a parameter to another function, or set a variable to store it, like this:

var someFunction = function() {
    alert("Un-Named function");
}

Here's how to pass it into another function and run it.

// define it
function iRunOtherFunctions(otherFunction) {
    otherFunction.call(this);
}

// run it
iRunOtherFunctions(function() {
    alert("I'm inside another function");
});

As David mentions below, you can instantly call it too:

(function() {
    alert("Called immediately");
})(); // note the () after the function.