CODEWITHSUNDEEP
javascript
tonyf
tonyf

Reputation: 35539

JavaScript NULL Values

I am getting the following JavaScript error:

'value' is null or not an object

Can someone please let me know what is the best way to check whether an object's value is NULL in JavaScript as I have been using:

if ((pNonUserID !== "") || (pExtUserID !== "")){

Is this correct or is there a better way?

Upvotes: 2

Views: 50137

Answers (4)

neeraj
neeraj

Reputation: 13

null, undefined and empty string is consider as false in conditional statement.

so

if(!n) alert("n is null or undefined or empty string"); 
if(n) alert("n has some value");

therefor, inflagranti suggested condition will work perfectly for you

if(pNonUserID && pExtUserID) { 

}

Upvotes: 0

Royce
Royce

Reputation: 552

The !== operator returns true when two variables are not the same object. It doesn't look at the values of the objects at all

To test if something is null:

myVar == null

Your code was testing to see if the variable 'pNonUserId' referred to the same object as "", which can never be true as "" will always be a new instance of the empty string.

As an aside, a test such as:

var n = something();
// do stuff
if (n)
  doSomethingElse();

Is a bad idea. If n was a boolean and false, but you were expecting the if block to test nullify you'll be in for a shock.

Upvotes: 3

Janick Bernet
Janick Bernet

Reputation: 21184

if (pNonUserID && pExtUserID)
{
   // neither pNonUserId nor pExtUserID are null here
}

Any Javascript variable automatically evaluates to true when it references an object.

What you were doing are comparisons to empty strings, which are not the same as null.

Upvotes: 0

Christian
Christian

Reputation: 28125

You don't have to do that:

var n=null;

if(n)alert('Not null.'); // not shown
if(!n)alert('Is null.'); // popup is shown

Your error implies otherwise:

var n=null;

alert(n.something); // Error: n is null or not an object.

In the case above, something like this should be used:

if(n)alert(n.something);

Upvotes: 13

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