If (array variable) syntax valid in Javascript

Question

I've been wondering about this syntax I picked up when attempting to accomplish some functionality using jQuery/javascript and was wondering if this is actually valid syntax or not. It seems to work, but it could be that javascript is just defaulting for true in the if-clause. I assumed it just validates whether or not the array has entries/is a valid array. Can anyone explain to me if the following is valid/invalid and if it is valid, what is it checking exactly?

var arrVariable = new Array();

... push things to array, etc.

if(arrVariable)    {
     ... doing stuff with array.    
}

Exactly what do you mean by valid array? If you are looking for elements in the array I would use arrVariable.length. — Spencer Wieczorek
– Spencer Wieczorek, Commented Jul 23, 2015 at 17:48

Alex Booker · Accepted Answer · 2015-07-23 17:56:12Z

3

if(arrVariable) {

}

This if statement evaluates if arrVariable is truthy or falsy.

The following values are always falsy:

false
0
""
null
undefined
NaN

All other values are truthy (source).

I assumed it just validates whether or not the array has entries/is a valid array.

This is not true. An empty array is an object and is therefore truthy. You can test this quite easily:

var arr = [];
if (arr) {
    console.log('arr is empty, but truthy, so this statement executes');
}

edited Jul 23, 2015 at 17:56

answered Jul 23, 2015 at 17:47

Alex Booker

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2 Comments

wwwmarty Over a year ago

Also note that "false" is truthy, while false is not.

DasianSensation Over a year ago

Oh wow, I never knew there was such a thing as "truthy" or "falsy" in javascript. Thanks for the answer and explanation!

lshettyl · Accepted Answer · 2015-07-23 18:36:12Z

0

var arr = ["one", "two"];

Check if the array has entries in it:

if (arr.length) {
    //There is at least one entry in the array
}

To check if it's an array:

if (arr instanceof Array) {
    //It's an array
}

answered Jul 23, 2015 at 18:36

lshettyl

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