How to do Null value check in Java script?

Question

in jsp i am writing java script. Please help me how to do null check in javascript? i have drop down list. onchange some action should happen. pleae find below code.

<select onchange="openPage(this.value)">

here some times this.value can be null. simply i need to do null check.when it is not null then only it should call openPage() method. please help me how to solve?

Thanks!

<select onchange="javascript:if(this.value !== null) openPage(this.value)"> ? — Cipi
– Cipi, Commented Oct 17, 2011 at 12:22

WickyNilliams · Accepted Answer · 2012-06-05 15:16:39Z

3

the simplest way to do this, and it covers cases where the value is an empty string, false, null, zero or undefined is:

if(!this.value) {
   //this will only execute if this.value is null, undefined, zero, empty string or false
}

Hope that helps. Obviously this isn't a good idea when it comes to working with boolean values (where you genuinely expect true or false values), but for 99% of the time it's great :)

edited Jun 5, 2012 at 15:16

answered Oct 17, 2011 at 12:21

WickyNilliams

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4 Comments

Freshblood Over a year ago

!'' is returns true but you said for empty strings too ?

WickyNilliams Over a year ago

Argh, Boolean logic fail! What I meant was it will only execute if this.value is null, undefined etc. The code is correct, the comment was not. Updated answer to reflect your observation. Thanks

Freshblood Over a year ago

I always hate to check null,undefined and empty strings together in javascript :). It is better to encapsulate these checks in a function.

WickyNilliams Over a year ago

I just like to embrace the truthy/falsey nature of JavaScript. For most instances empty strings, null or undefined require similar handling - consider string.IsNullOrEmpty or string.IsNullOrWhitespace in .NET. So I find it makes sense to group the logically as above, keeps your code quite terse as well

Pranay Rana · Accepted Answer · 2012-02-08 05:38:56Z

1

(this.value == undefined)

Do check as above

edited Feb 8, 2012 at 5:38

answered Oct 17, 2011 at 12:21

Pranay Rana

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1 Comment

WickyNilliams Over a year ago

i was going to say, i've never seen the is operator in JS. Am i missing something here??

animuson · Accepted Answer · 2011-12-15 00:59:27Z

0

Try using this:

if(this.value != null)

edited Dec 15, 2011 at 0:59

animuson♦

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answered Oct 17, 2011 at 12:25

Royi Namir

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