Does assigning a function to a variable in javascript run the function

Question

I have three simple programs below with different outputs. I am a bit confused as to why I get a different output. What really happens when you assign a function to a variable? Does it not run unless you have parentheses (i.e. myfunction())? I'm also very confused as to how JavaScript allows the parenthesis behind a function as 'optional' when calling it. Can someone clear this up? I only know Java so this is all new territory for me.

// ------First--------------------------------
var x = 9;
function myfunction (){
  x = 3;
}
var w = myfunction;
w();
console.log(x);
//output is 3


// ---------Second -----------------------------
var x = 9;
function myfunction (){
  x = 3;
}
var w = myfunction;
console.log(x);
//output is 9


// ---------Third -----------------------------
var x = 9;
function myfunction (){
  x = 3;
}
var w = myfunction();
console.log(x);
//output is 3

Pointy · Accepted Answer · 2013-12-11 17:11:35Z

4

No, it does not. A reference to a function by name is simply a reference to a value, like any other value. Without the () operator, it's not a function call.

Parentheses are not optional when calling a function except when it's being called via the new operator. Thus:

function foo() {
  console.log("hi!");
}

var otherFoo = foo; // no function call
var obj = new foo;  // function call via "new"
var x = foo();      // function call via "()"

edited Dec 11, 2013 at 17:11

answered Dec 11, 2013 at 17:00

Pointy

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1 Comment

user3092075 Over a year ago

Thanks Pointy. Can you please give an example of the "new operator" and how the call would happen...

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