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As the question suggest, when should I use

Example A (function declaration):

function abc(){
  // some code
}

abc();

over Example B (function expression):

var abc = function(){
  // some code
}

abc();

and vice versa.

I know they are different in nature but they basically just do the same thing (correct me if they're not), right?

So how to I decide which one should I use?

EDIT :

I know for Example A, the function can be called whenever wherever intended due to hoisting.

What I actually want to know is what makes you decide to use Example A or Example B.

yqlim
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  • The variable version cleanable and must be defined before calling the other one is not. that as my knowledge. – Mamdouh Saeed Nov 08 '16 at 04:16
  • you would need the `var abc = function()` declaration, when you need to pass your function as a callback to any other function. – Jerin Joseph Nov 08 '16 at 04:17
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    @JerinJoseph both of them support this feature. – Mamdouh Saeed Nov 08 '16 at 04:20
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    Possible duplicate of [JavaScript function declaration syntax: var fn = function() {} vs function fn() {}](http://stackoverflow.com/questions/336859/javascript-function-declaration-syntax-var-fn-function-vs-function-fn) – Thilo Nov 08 '16 at 04:26
  • @Thilo I didn't find an answer there. which is why i decided to ask a new question. Thanks for pointing that out tho! – yqlim Nov 08 '16 at 05:33

2 Answers2

1

If you want to call abc() before defining the function, only the first pattern will work.

The variable declaration does get hoisted, too, but not the assignment, so it will be undefined, whereas the function will already be complete with its body.

I guess I would use the var pattern only if I intend to re-assign it later.

Thilo
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Generally, you should use the function declaration syntax when possible. The best reason is that if you define the function in the code after its use, the code will still work.

stuff();

function stuff() {
    console.log("hello");
}

will work, but

stuff();

var stuff = function() {
    console.log("hello");
}

will not.

When you are passing an anonymous function to another function, you use a function expression.

doSomething(function() {
    console.log("done");
});

Otherwise, both work.

afuous
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