functionDeclarations.md

Anonymous vs. referenced vs. declared functions

Anonymous

Anonymous functions are typically used as callbacks.

function takesACallback(callback) {
    // do some interesting things here
    return "The callback says: " + callback();
}

takesACallback(function() {
    return "I'm the callback!";
}); // returns "The callback says: I'm the callback!"

See the function that’s a parameter to the takesACallback call? Notice that it doesn’t have a name? That’s an anonymous function.

Referenced

However, you can still have a reference to an anonymous function, just because it is unnamed it doesn’t mean it’s unreferenced. Also it's called function expression.

var reference = function() {
    return "I'm still an anonymous function";
}

reference(); // returns "I'm still an anonymous function"

The function itself is still anonymous (it doesn’t have a name directly attached to it), but you can call the function by the named reference. Function expressions are not hoisted like function declarations decribed below.

Declared

Declared functions are not anonymous. They have a name directly attached to the function, with no need for a named reference.

function declared() {
    return "I'm not anonymous function";
}

declared(); // returns "I'm not anonymous function"

Writing a named function like this results in a function declaration which if hoisted to the top of the file.