## 二分法查找 前提：数组有序 ``` const arr = [1,3,5,6,7,9,10] function binarySearch (arr, target) { let start = 0 let end = arr.length - 1 let middle let curElement while (start <= end) { middle = Math.floor((start + end) / 2) curElement = arr[middle] if (curElement === target) { return middle } else if (curElement > target) { end = middle - 1 } else { start = middle + 1 } } return -1 } console.log(binarySearch(arr, 5)) ```