What is the simplest way I can check to see if an array has elements or not?

Question

How can I determine if an array has elements and return false if that array is not defined?

I have the array modal.questions

I was using modal.questions.length but now this seems to be a problem if questions is not defined.

Is there a way I can do this using a libray function of _underscore.js or a simple way I can code a function to make the check?

@Felix King It is similar but not an exact duplicate The alleged duplicate question considers a zero length array to be valid. The current question does not. Detecting zero length arrays requires more esoteric Javascript like instanceOf — Paul, Aug 22 '13 at 11:13
@Melina -- Or actualy, your question might be vague. Did you know you can have perfectly good defined array, that is empty, like `A=[];` . Do you want `true` or `false` with that? — Paul, Aug 22 '13 at 11:16

score 1 · Answer 1 · answered Aug 22 '13 at 10:41

1

if(modal.questions && modal.questions.length > 0) {}

should work.

answered Aug 22 '13 at 10:41

Tiele Declercq

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score 0 · Answer 2 · answered Aug 22 '13 at 10:41

0

check if(modal.questions === undefined) first, then do your length check.

Note: in some older browsers it was possible to overwrite value of undefined. In such case a safe check would be if(modal.questions === void 0) as void 0 will return actual undefined value. If however you're targetting modern browsers, you need not worry about that.

answered Aug 22 '13 at 10:41

Mchl

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If array is null, or for some reason it is not an array, then checking length may throw an error. – Paul Aug 22 '13 at 11:09

score 0 · Answer 3 · answered Aug 22 '13 at 10:41

0

try like this:

if (typeof array !== 'undefined' && array.length > 0) {
    // existss and have one item
}

answered Aug 22 '13 at 10:41

Davor Mlinaric

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When `array = null` it throws `TypeError Cannot read property 'length' of null` – Paul Aug 22 '13 at 11:04

M. Abbas · Accepted Answer · 2013-08-22T12:31:55.530

0

function isEmpty(theArray) {
    return theArray == null || theArray.length <= 0;
}

edited Aug 22 '13 at 12:31

answered Aug 22 '13 at 10:44

M. Abbas

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this does not work if i pass a null – bhb Aug 22 '13 at 11:21

bhb · Answer 5 · 2013-08-22T11:33:06.423

This works in all the browsers

if(!Array.isArray) {
  Array.isArray = function (vArg) {
    return Object.prototype.toString.call(vArg) === "[object Array]";
  };
}

//add length check also here
function isEmpty(theArray) {
    return Array.isArray(theArray)    
}

var a = new Array();
var b = null;
var c = undefined;
var d = [];

alert(isEmpty(a)); //true
alert(isEmpty(b)); //false
alert(isEmpty(c)); //false
alert(isEmpty(d)); //true

JSFiddle

Source :)

What is the simplest way I can check to see if an array has elements or not?

5 Answers5