费舍尔·耶茨的Java随机播放

Question

New to JS and currently learning in college. For my current JS project, I am building a memory card game. I started to think on how to randomly shuffle the cards, and I got close to what Fisher–Yates Shuffle algorithm does - the second program on this page . However, I don't understand what the [0] does after the splice method exactly. Is it what shifts/compacts the array? If yes, I can't find other examples/documentations about that.

function shuffle(array) {
  var copy = [], n = array.length, i;

  // While there remain elements to shuffle…
  while (n) {

    // Pick a remaining element…
    i = Math.floor(Math.random() * n--);

    // And move it to the new array.
    copy.push(array.splice(i, 1)[0]);
  }

  return copy;
}

Answer 1

array.splice(i, 1) cuts out the i -th element of array and returns it as a single-value array (just like array.splice(i, 2) would cut out i -th and i+1 -th element and return them as a two-element array). Then [0] , the simple indexing operation, picks that single element from that array (as we don't need an array); this single element is then added to copy using copy.push .

More familiar uses of the indexing operation:

array = [4, 7, 2, 10];
array[0]
// => 4
array[1]
// => 7

array = [18];
array[0]
// => 18

Answer 2

array.splice() returns an array, but while shuffling you want to take a random card from an unknown position and put it inside the new array(shuffled one). Now the catch is you don't want to add the similar array again by doing copy.push(array.splice(i, 1) as this will add the entire returned array to copy array and the randomness of your shuffle will get reduced which in turn will cause dependent result in your game because the array will be similar(~) to last one with just few bits flipped. Adding [0] to array.splice(i, 1) ensures that you are only copying one element from the entire result array returned at time, which results in greater randomness.