How to display something if variable is not set inside a each loop?

Question

$.each(json.data,function(i,fb){

//some code here...

if (msg.length > 150) {
                msg = msg.substr(0,200)+"...";
            }

//more code here...
});

I have an issue here. If msg is not defined I got an error and I got nothing displayed on the browser.

Possible Solution: create a default message for the cases where msg is not defined.

Try:

if (msg = 'undefined') {
 msg = 'some default message';
} else if (msg.length > 150) {
msg = msg.substr(0,200)+"...";
}

Issue: The above try didn't work because I get for each item, the same default message, instead of having the default message only for those cases were msg is no "set".

Request: Can I have your help in order to write the proper code so that, on each item, if msg is not defined show a default one, if otherwise, it's site, display it ?

If you lack some information in order to proper help me, please, let me know. I'm really on a bad position right now. :s

Thanks a lot, MEM

is msg the JSON data you received from your webservice? Another thing I noticed is your statement should be with the == if(msg == 'undefined'). maybe post your entire AJAX call to get more context. — webdad3
– webdad3, Commented Jan 4, 2011 at 15:58

Jakob · Accepted Answer · 2011-01-04 15:58:30Z

3

You have to write == rather than = in your if-statement. Also, if you're trying to test if it's undefined, you should use typeof, like this:

if (typeof msg == 'undefined')

This idea of comparing it using typeof is actually safer than comparing it to the object called undefined. The reason is that the object can be redefined, but the result of typeofnever changes. I dont know why anyone would be crazy enough to do it, but it is possible to write:

undefined = "hi there";
if (msg == undefined) // oh noes!
  ...
if (typeof msg == "undefined") // still works!

answered Jan 4, 2011 at 15:58

Jakob

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Nikita Rybak · Accepted Answer · 2011-01-04 15:56:43Z

3

if (msg = 'undefined') {

-->

if (msg == undefined) {

Two things

We use == to compare objects and = to assign variables. Even in javascript.
'undefined' is a string with text 'undefined'. undefined (without quotes) is a global object in javascript. Or maybe not global object, but whatever it is you can use it to check whether variable exists.

answered Jan 4, 2011 at 15:56

Nikita Rybak

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3 Comments

MEM Over a year ago

Thank you! :) (I will run now with shame). :)

Jakob Over a year ago

This solution works for any sane situation, but it's not the recommended way to test for undefined..

David Mårtensson Over a year ago

undefined is not the same as null, you can pass null to a function but you cannot pass undefined to a function. Use typeof msg == "undefined" instead

stef · Accepted Answer · 2011-01-04 15:57:51Z

1

if (msg == undefined) ...

The trick is to use == (comparison) versus = (actually sets the variable).

answered Jan 4, 2011 at 15:57

stef

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