Method vs Functions, and other questions

Question

With respect to JS, what\'s the difference between the two? I know methods are associated with objects, but am confused what\'s the purpose of functions? How does the syntax

Answer 1

Your first line, is creating an object that references a function. You would reference it like this:

myFirstFunc(param);

But you can pass it to another function since it will return the function like so:

function mySecondFunction(func_param){}
mySecondFunction(myFirstFunc);

The second line just creates a function called myFirstFunc which would be referenced like this:

myFirstFunc(param);

And is limited in scope depending on where it is declared, if it is declared outside of any other function it belongs to the global scope. However you can declare a function inside another function. The scope of that function is then limited to the function its declared inside of.

function functionOne(){
    function functionTwo(){}; //only accessed via the functionOne scope!
}

Your final examples are creating instances of functions that are then referenced though an object parameter. So this:

function myFirstFunc(param){};

obj.myFirst = myFirstFunc(); //not right!
obj.myFirst = new myFirstFunc(); //right!

obj.myFirst('something here'); //now calling the function

Says that you have an object that references an instance of a function. The key here is that if the function changes the reference you stored in obj.myFirst will not be changed.

While @kevin is basically right there is only functions in JS you can create functions that are much more like methods then functions, take this for example:

function player(){

    this.stats = {
        health: 0,
        mana: 0,

        get : function(){
            return this;
        },

        set : function( stats ){
            this.health = stats.health;
            this.mana = stats.mana;
        }  
}    

You could then call player.stats.get() and it would return to you the value of heath, and mana. So I would consider get and set in this instance to be methods of the player.stats object.

Answer 2

var myFirstFunc = function(param) {
    //Do something
};

and

function myFirstFunc(param) {
    //Do something
};

are (almost) identical. The second is (usually) just shorthand. However, as this jsfiddle (http://jsfiddle.net/cu2Sy/) shows, function myFirstFunc will cause the function to be defined as soon as the enclosing scope is entered, whereas myFirstFunc = function will only create it once execution reaches that line.

As for methods, they have a this argument, which is the current object, so:

var obj = {};
obj.func = function( ) {
    // here, "this" is obj
    this.test = 2;
}
console.log( obj.test ); // undefined
obj.func( );
console.log( obj.test ); // 2

The exact syntax you showed is because you can also do this:

function abc( ) {
    this.test = 2;
}
var obj = {};
obj.func = abc;
obj.func( ); // sets obj.test to 2

but you shouldn't without good reason.