How to create an if statement in javascript that will run if a variable is undefined?

Question

Possible Duplicate:
Detecting an undefined object property in JavaScript

Would it be like this?

if(variable == undefined) {

or would it be like this?

if(variable == "undefined") {

score 6 · Answer 1 · answered Aug 23 '10 at 17:36

6

if(typeof(variable) == 'undefined')

answered Aug 23 '10 at 17:36

Atul Dravid

1

You don’t need the parentheses as `typeof` is an operator and not a function. – Gumbo Aug 23 '10 at 17:39
1

@chromedude See here: https://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Operators/Special_Operators/typeof_Operator – Tim Goodman Aug 23 '10 at 17:41
ya you are right Gumbo... sorry about that :) was in a hurry when i answered :P – Atul Dravid Aug 23 '10 at 20:12

score 6 · Accepted Answer · answered Aug 23 '10 at 17:37

6

if (typeof variable == 'undefined')

answered Aug 23 '10 at 17:37

score 1 · Answer 3 · answered Aug 23 '10 at 17:37

1

Use the typeof operator here, like this:

if(typeof variable == "undefined") {

answered Aug 23 '10 at 17:37

Nick Craver

Why would you add an extra call to `typeof` when simply checking `variable == undefined` works? – Justin Niessner Aug 23 '10 at 17:42
@Justin - `undefined` may be redefined, for example: http://jsfiddle.net/nick_craver/gHjg5/ – Nick Craver Aug 23 '10 at 17:51

score 0 · Answer 4 · answered Aug 23 '10 at 17:36

0

if(variable == undefined) {

answered Aug 23 '10 at 17:36

NicolasT

score 0 · Answer 5 · answered Aug 23 '10 at 17:37

0

The first one

if (variable == undefined) {}

answered Aug 23 '10 at 17:37

Jemes

5 Answers5