Checking Array Emptiness with Javascript

Question

Is there a way to determine the following JavaScript array is empty without manually iterating through it?

var js_array = Array("", "", "", "")

I suppose you could test if js_array.join('') is true or false, but that leaves open a bunch of false positives. The fact is, that array isn't "empty", and you have to define exactly what you want to test for first. — Blazemonger
– Blazemonger, Commented Dec 30, 2015 at 21:14
You could filter and only return elements that are truthy then check the length of the array. — disappointed in SO leadership
– disappointed in SO leadership, Commented Dec 30, 2015 at 21:15
@dandavis—probably better to use Boolean to make the type conversion explicit (thought it's one more character to type). — RobG
– RobG, Commented Jan 2, 2016 at 10:10

guyaloni · Accepted Answer · 2015-12-30 21:52:13Z

4

I guess you want to check whether array contains some non-empty strings.

Use filter to remove empty strings:

var tmp_js_array = js_array.filter(Boolean)

(see filter documentation)

Then you can check whatever you want - in your case tmp_js_array will be empty.

edited Dec 30, 2015 at 21:52

answered Dec 30, 2015 at 21:16

guyaloni

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2 Comments

RobG Over a year ago

That doesn't actually check whether the array contains non–empty strings, it just removes members where ToBoolean returns false. At least a further check is required to see if the new array is the same length as the old.

guyaloni Over a year ago

You are right, since I don't know exactly what @Calvin wants to check I left this for him... (tmp_js_array.length == 0 will do the work for example)

RobG · Accepted Answer · 2015-12-30 21:22:15Z

1

There is Array.protoype.every, which can be used to test whether every value meets a test and returns false for the first that doesn't. So if your definition of "empty" is that all members are empty strings, then:

['','','',''].every(function(v){return !/\S/.test(v)}); // true

will return true if every member does not contain any non–whitespace characters. Alternatively, you can use some to see if any member contains a non–whitespace character and negate the result:

!['','','',''].some(function(v){return /\S/.test(v)});

answered Dec 30, 2015 at 21:22

RobG

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