Clear explanation of .sort() behavior for this case

Question

alert("0123456789".split("").sort(function(){return .5-Math.random()}).join(""));

This is probably one of the shortest ways to generate a 10-digit number in JavaScript that contains 10 digits from 0 to 9 in the randomized order. Example: 7205169483.

split("")//OK, it splits by chars because of empty separator
.sort(function(){return .5-Math.random()})
.join("")//joins with empty string as a separator

Why doesn't {return Math.random()} work?

How many times .sort() is executed - ten or one?

Did you look at the definition of the `sort` function ? What is expected from the callback ? — Denys Séguret, Jan 06 '14 at 16:20
Why downvote? A doubt is a fare doubt, might be the user would have missed some thing. As some might not always be perfect. — Nagaraj Tantri, Jan 06 '14 at 16:22
possible duplicate of [Is it correct to use JavaScript Array.sort() method for shuffling?](http://stackoverflow.com/questions/962802/is-it-correct-to-use-javascript-array-sort-method-for-shuffling) — Bergi, Jan 06 '14 at 17:54

score 0 · Answer 1 · edited May 23 '17 at 12:11

As it has been said in the comments by @elclanrs, sort expects a callback function that will take two elements a and b and compare them. This function must return a negative number if a < b, 0 if a == b and a positive number otherwise.

The function sort will be called a number of times that depends on the implementation of the sorting algorithm. You can find more information in this question.

In your example, 0.5 - Math.Random() will return a negative, or a positive number, because Math.Random() returns a value between 0 and 1.

Clear explanation of .sort() behavior for this case

1 Answers1