what are the various ways to define function in javascript [duplicate]

Question

Which is is the best way to define a function in javascript . how to define a function using ':' like function_Name : function(){} .

Answer 1

Hope this will be useful

Named function

function someName(){
 //rest of code
}

can be called by someName();

Function expression

var someName = function(){}

can be called by someName()

IIFE

(function(someParam){
 //rest of code
}(params))

IIFE can also can also written in this way

+function(someParam){
//rest of code
}(someParam)

Named function expression

var someVar = function someFoo(){};

this is called by someVar() . someFoo is only accessible inside itself

Arrow function(aka fat arrow)

var someVar= (param1, param2) => {return somereturn}

Function constructor

var adder = new Function('a', 'b', 'return a + b');

Beside this you can also take a look at call & apply

Answer 2

There is no "best" way to define a function, it depends on your needs. For example if you have a function that validates something it makes sense to put it into a variable like Pugazh said:

var foo = function(){
  if (/*some condition*/) {
    //do something...;
    return true;
  }
  else {
    return false;
  }

And then use it like alert(foo()); and it will execute the function and return the value (true or false). Sometimes you want a named function you can call with options like:

function SaveData(data) {
    //Code to save something
}

And then call it like SaveData("Hello World");

And sometimes you just add a function without a name that is executed as a callback (e.g. in jquery) or when you perform a specific action but you define it at the event and not as a named function.

All types of functions have their use cases.