SOURCE

 // 二分算法实现
 function binarySearch (arr, target) {
    let left = 0;
    let right = arr.length - 1;
    while(left <= right) {
        let min = parseInt((left + right) / 2);
        if(arr[min] == target) {
            return min;
        }else if(arr[min] < target) {
            left = min + 1;
        }else if(arr[min] > target) {
            right = min - 1;
        }
    }
    return -1;
}
let a = [1,2,3,4,5,6,7,8,9,10,50,59,76,100];
console.log(binarySearch(a, 59));