Should I check array length when using sort method in JavaScript?

Question

I have a question about array.sort() method in JavaScript. Set of values in the array can vary from 1 to more. Sort function should sort them in the order if there is more than one element. Here is my code:

var myDates = ["03/05/2017","02/01/2017","03/02/2017"];

myDates.sort(function(a,b) {
    a = a.split('/').reverse().join('');
    b = b.split('/').reverse().join('');
    return a > b ? 1 : a < b ? -1 : 0;
});

Code above works fine, all dates are sorted. My question is should I check the length of the array before I run the sort method? I'm asking this because my array can have one element only in some situations. So far my code did not throw any errors when I tested with one element only, but I would like to know if I should check the length of the array before I run the sort() or JavaScript already takes care of that? If anyone knows the answer please let me know. Thank you.

well ... check what happens yourself, for both 0 and 1 element - hint, put a console.log inside the callback — Jaromanda X
– Jaromanda X, Commented Mar 8, 2017 at 3:03
How that will help me to get the answer? I know what my function will produce if I have more than one element but I'm wondering if I should prevent my function running if I have less than two elements. — espresso_coffee
– espresso_coffee, Commented Mar 8, 2017 at 3:10
fine ... if there's less than 2 elements, the sort callback is not even called - so, there's no need for you to check the length. Honestly, I just thought you may want to learn how to learn — Jaromanda X
– Jaromanda X, Commented Mar 8, 2017 at 3:12
I tried but console.log() did not produce any output inside of the call back function. Thanks for explaining. — espresso_coffee
– espresso_coffee, Commented Mar 8, 2017 at 3:31

fubar · Accepted Answer · 2017-03-08 03:16:43Z

1

This behaviour is documented in the Array.prototype.sort specification. See http://www.ecma-international.org/ecma-262/6.0/#sec-array.prototype.sort

Specifically:

The arguments for calls to SortCompare are values returned by a previous call to the [[Get]] internal method, unless the properties accessed by those previous calls did not exist according to HasOwnProperty. If both perspective arguments to SortCompare correspond to non-existent properties, use +0 instead of calling SortCompare. If only the first perspective argument is non-existent use +1. If only the second perspective argument is non-existent use −1.

In short:

Array.prototype.sort((undefined, undefined) => { ... }); // => 0

Array.prototype.sort((undefined, b) => { ... }); // => 1

Array.prototype.sort((a, undefined) => { ... }); // => -1

answered Mar 8, 2017 at 3:16

fubar

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2 Comments

fubar Over a year ago

No, it is relevant. If both perspective arguments to SortCompare correspond to non-existent properties, use +0 instead of calling SortCompare...

Jaromanda X Over a year ago

sorry, I see what you're saying - your code used undefined which confused me - will remove my "critique" :p

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