Array API: array.sort() can take a compare function

[].sort() can take a compare function

the compare function

can be given as the only parameter to sort() (and gets used by it)

let compareFunctionUsed; const compare = () => { compareFunctionUsed = true }; [2, 1].sort(); assert.equal(compareFunctionUsed, true);

is called with two values to be compared

let parameters = []; const compare = (...args) => {parameters = ____;}; [2, 1].sort(compare); assert.ok(parameters.includes(1)); assert.ok(parameters.includes(2));

is called multiple times (depending how the sort algorithm is implemented)

let callCount = 0; const compare = () => {callCount--}; [3, 1, 2].sort(); assert.ok(callCount > 1);

the return value of the compare function indicates how the two values compare

examples

sort numbers

const numericCompare = (a, b) => 0; assert.deepEqual([1, 11, 2].sort(numericCompare), [1, 2, 11]);

sort number-like values

const ensuredNumericCompare = () => {}; assert.deepEqual(['1', '23', 2, ' 3 '].sort(ensuredNumericCompare), ['1', 2, ' 3 ', '23']);

custom compare algorithm

const monthOrder = ['Jan', 'Feb', 'Mar', 'Apr', 'May']; const monthCompare = (a, b) => a + b; assert.deepEqual(['May', 'Apr', 'Feb'].sort(monthCompare), ['Feb', 'Apr', 'May']);

Links

mdn docs Very detailed description of how `sort()` works.
announcement Announcement of this kata on twitter.

Required Knowledge

• `array.sort()` basics (Array API)

Related Katas

Array API

• array.sort() basics
• array.sort() can take a compare function
• array.shift() (as introduced in ES3)
• array.push() (as introduced in ES3)
• Array.from()
• Array.of()
• array.fill()
• array.find()
• array.findIndex()
• array.entries()
• array.keys()
• array.values()
• array.includes()
• array.toReversed()

Difficulty Level

INTERMEDIATE

First Published

23 October 2015

Stats

9 tests to solve