Javascript: How to test if response JSON array is empty

Question

I'm getting back the following JSON:

{"array":[],"object":null,"bool":false}

And I'm testing it with the following, seemingly exhaustive, if statement:

$.ajax({
        type: "GET",
        url: "/ajax/rest/siteService/list",
        dataType: "json",
        success: function (response) {
            var siteArray = response.array;

            // Handle the case where the user may not belong to any groups
            if (siteArray === null || siteArray=== undefined || siteArray=== '' || siteArray.length === 0) {
                            window.alert('hi');
            }
       }
});

But the alert is not firing. :[

[]. I tried if siteArray === "[]" but that didn't work either — Lurk21
– Lurk21, Commented May 3, 2013 at 2:25
An empty array is not the same as null, undefined, et al. — Phrogz
– Phrogz, Commented May 3, 2013 at 2:25

Arun P Johny · Accepted Answer · 2013-05-03 02:33:38Z

28

Use $.isArray() to check whether an object is an array. Then you can check the truthness of the length property to see whether it is empty.

if( !$.isArray(siteArray) ||  !siteArray.length ) {
    //handler either not an array or empty array
}

answered May 3, 2013 at 2:33

Arun P Johny

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2 Comments

Lurk21 Over a year ago

That did it, and it's much more elegant

Dennis Over a year ago

That's an unfortunate resolution to the question. Why does this work but OP's code didn't?

Phrogz · Accepted Answer · 2013-05-03 02:27:02Z

7

Two empty arrays are not the same as one another, for they are not the same object.

var a = [];
if (a === []){
  // This will never execute
}

Use if (siteArray.length==0) to see if an array is empty, or more simply if (!siteArray.length)

answered May 3, 2013 at 2:27

Phrogz

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2 Comments

Phrogz Over a year ago

@Dennis Good point, it was scrolled off the window and I didn't see it. Nonetheless, it will work for an empty array. More data is needed :/

MattieG4 Over a year ago

I was wondering why my comparison wasn't working. That makes a lot of sense thank you.

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