含义：自己调自己

递归三要素：定义函数、终止条件和等价关系式

小案例：排序

        let arr1 = [8, 8, 9, 13, 45, 8, 0, 1, 9, 66];//定义函数function quickSort(arr) {//终止条件if (arr.length <= 1) return arr;const baseIndex = Math.floor(arr.length / 2);console.log(baseIndex);const baseVal = arr.splice(baseIndex, 1)[0];console.log(baseVal);const left = [];const right = [];for (let i = 0; i < arr.length; i++) {if (arr[i] < baseVal) {left.push(arr[i]);} else {right.push(arr[i])}}//等价关系式    return quickSort(left).concat(baseVal, quickSort(right));}console.log(quickSort(arr1));