1. /**
    2.  * Copies the values of `source` to `array`.
    3.  *
    4.  * @private
    5.  * @param {Array} source The array to copy values from.
    6.  * @param {Array} [array=[]] The array to copy values to.
    7.  * @returns {Array} Returns `array`.
    8.  */
    9. function copyArray(source, array) {
    10.   let index = -1
    11.   const length = source.length
    13.   array || (array = new Array(length))
    14.   while (++index < length) {
    15.     array[index] = source[index]
    16.   }
    17.   return array
    18. }
    20. /**
    21.  * Creates an array of shuffled values, using a version of the
    22.  * [Fisher-Yates shuffle](https://en.wikipedia.org/wiki/Fisher-Yates_shuffle).
    23.  *
    24.  * @since 0.1.0
    25.  * @category Array
    26.  * @param {Array} array The array to shuffle.
    27.  * @returns {Array} Returns the new shuffled array.
    28.  * @example
    29.  *
    30.  * shuffle([1, 2, 3, 4])
    31.  * // => [4, 1, 3, 2]
    32.  */
    33. function shuffle(array) {
    34.   const length = array == null ? 0 : array.length
    35.   if (!length) {
    36.     return []
    37.   }
    38.   let index = -1
    39.   const lastIndex = length - 1
    40.   const result = copyArray(array)
    41.   while (++index < length) {
    42.     // 求一个 lastIndex 到 index 之间的随机值
    43.     const rand = index + Math.floor(Math.random() * (lastIndex - index + 1))
    45.     // 交换两个值
    46.     const value = result[rand]
    47.     result[rand] = result[index]
    48.     result[index] = value
    49.   }
    50.   return result
    51. }
    1. function shuffle(array) {
    2.   var m = array.length, t, i;
    4.   // While there remain elements to shuffle…
    5.   while (m) {
    7.     // Pick a remaining element…
    8.     i = Math.floor(Math.random() * m--);
    10.     // And swap it with the current element.
    11.     t = array[m];
    12.     array[m] = array[i];
    13.     array[i] = t;
    14.   }
    16.   return array;
    17. }