When checking if an array is empty, should I use array.length <= 0 or array.length === 0?

Question

I am used to check for empty arrays with array.length <= 0. Of course the array should never have a length smaller than 0. This is a habit I developed to make sure my program runs "just in case something weird happens". Is there any reason not to use the <= operator and use === 0 instead?

Also, you can use just !list.length. For empty list, this will return true, else false. — palaѕн
– palaѕн, Commented Mar 10, 2020 at 8:18
No need for strict comparison(===), in Javascript Array.length is type of positive number. So using == is fine. But if your array is undefined then you may end up in error, so it is better to check that also. Hope this helps. — R.Sarkar
– R.Sarkar, Commented Mar 10, 2020 at 8:21

CertainPerformance · Accepted Answer · 2020-03-10 08:17:12Z

4

If the list is an array, then no, there's no chance of the length being anything other than a whole number. From the specification:

Every Array object has a non-configurable "length" property whose value is always a nonnegative integer less than 2 ** 32

Given an array object, you couldn't even deliberately make things confusing by changing the length to something other than a valid length; an error will be thrown:

const arr = [];
Object.defineProperty(arr, 'length', { value: -5 })

answered Mar 10, 2020 at 8:17

CertainPerformance

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T.J. Crowder Over a year ago

Of course, when you're dealing with proxies or array-likes... But if someone's creating an array proxy that returns a negative number for length, or creating an array-like with a negative length, there are other issues... :-)

StepUp · Accepted Answer · 2020-03-10 08:16:45Z

2

In my view, there is no reason to check negative value of length list.length <= 0. as specs for Arrays says:

Every Array object has a length property whose value is always a nonnegative integer less than 2³².

So it is perfectly eligible to check list.length === 0

answered Mar 10, 2020 at 8:16

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