一、冒泡排序

写法一
function bubbleSort(arr) {
    var len = arr.length;
    for (var i = 0; i < len; i++) {
        for (var j = 0; j < len - 1 - i; j++) {
            if (arr[j] > arr[j+1]) {        //相邻元素两两对比
                var temp = arr[j+1];        //元素交换
                arr[j+1] = arr[j];
                arr[j] = temp;
            }
        }
    }
    return arr;
}

写法二
const Compare = {
  LESS_THAN: -1,
  BIGGER_THAN: 1,
  EQUALS: 0
};
function defaultCompare(a, b) {
  if (a === b) {
    return Compare.EQUALS;
  }
  return a < b ? Compare.LESS_THAN : Compare.BIGGER_THAN;
}
function swap(array, a, b) {
  /* const temp = array[a];
  array[a] = array[b];
  array[b] = temp; */
  [array[a], array[b]] = [array[b], array[a]];
}
function bubbleSort(array, compareFn = defaultCompare) {
  const { length } = array;
  for (let i = 0; i < length; i++) {
    for (let j = 0; j < length - 1; j++) {
      if (compareFn(array[j], array[j + 1]) === Compare.BIGGER_THAN) {
        swap(array, j, j + 1);
      }
    }
  }
  return array;
}

二、选择排序

方法一
function selectionSort(arr) {
    var len = arr.length;
    var minIndex, temp;
    for (var i = 0; i < len - 1; i++) {
        minIndex = i;
        for (var j = i + 1; j < len; j++) {
            if (arr[j] < arr[minIndex]) {     //寻找最小的数
                minIndex = j;                 //将最小数的索引保存
            }
        }
        if(i !== minIndex) {
            temp = arr[i];
            arr[i] = arr[minIndex];
            arr[minIndex] = temp;
        }
        
    }
    return arr;
}

写法二
const Compare = {
  LESS_THAN: -1,
  BIGGER_THAN: 1,
  EQUALS: 0
};
function defaultCompare(a, b) {
  if (a === b) {
    return Compare.EQUALS;
  }
  return a < b ? Compare.LESS_THAN : Compare.BIGGER_THAN;
}
function swap(array, a, b) {
  /* const temp = array[a];
  array[a] = array[b];
  array[b] = temp; */
  [array[a], array[b]] = [array[b], array[a]];
}
function selectionSort = (array, compareFn = defaultCompare) => {
  const { length } = array;
  let indexMin;
  for (let i = 0; i < length - 1; i++) {
    indexMin = i;
    for (let j = i; j < length; j++) {
      if (compareFn(array[indexMin], array[j]) === Compare.BIGGER_THAN) {
        indexMin = j;
      }
    }
    if (i !== indexMin) {
      swap(array, i, indexMin);
    }
  }
  return array;
};

三、插入排序

function insertionSort(arr) {
    var len = arr.length;
    var preIndex, current;
    for (var i = 1; i < len; i++) {
        preIndex = i - 1;
        current = arr[i];
        while(preIndex >= 0 && arr[preIndex] > current) {
            arr[preIndex+1] = arr[preIndex];
            preIndex--;
        }
        arr[preIndex+1] = current;
    }
    return arr;
}

四、归并排序

function mergeSort(arr) {  //采用自上而下的递归方法
    var len = arr.length;
    if(len < 2) {
        return arr;
    }
    var middle = Math.floor(len / 2),
        left = arr.slice(0, middle),
        right = arr.slice(middle);
    return merge(mergeSort(left), mergeSort(right));
}

function merge(left, right)
{
    var result = [];

    while (left.length && right.length) {
        if (left[0] <= right[0]) {
            result.push(left.shift());
        } else {
            result.push(right.shift());
        }
    }

    while (left.length)
        result.push(left.shift());

    while (right.length)
        result.push(right.shift());

    return result;
}