Understanding a Javascript Codewars challenge

Question

     var gimme = function (inputArray) {
     var order = inputArray.slice().sort(function(a,b) { return a-b;});
    return inputArray.indexOf(order[1]);
     };

This is a function to find the index number of the middle number in a sequence, when given a triplet of numbers. However I don't understand the section:

     (function(a,b) { return a-b;});

Could someone explain the purpose of this part? I would be very grateful. Thanks!

Community · Accepted Answer · 2020-06-20 09:12:55Z

3

This is an example from MDN:

var numbers = [4, 2, 5, 1, 3];
numbers.sort(function(a, b) {
    return a - b;
});
console.log(numbers);

The result is [1, 2, 3, 4, 5];

So this is a very simple comparator for integers.

Comparators works like the following:

if a < b, return a negative
if b < a, return a positive
in other cases, return zero

This function uses a simple mathematical property of integers.

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Aug 13, 2015 at 12:04

meskobalazs

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3 Comments

Huw Davies Over a year ago

Thanks so much! What do you mean when you say comparator?

meskobalazs Over a year ago

A Comparator is an object which compares other objects and decides whether one is "larger" or they are equal. For example the <= operator, is a partial sort comparator on the set of real numbers.

Huw Davies Over a year ago

Very helpful. Thank you.

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