JS二分法查找数值在数值中的区间

需求：求一个数字类型，在一个数组中的区间；

$(function(){
    //二分法计算最近的数组下标
    Array.prototype.binarySearch = function(obj){
        //var value = 0;
        var left = 0;
        var right = this.length;
        while(left <= right){
            var center = Math.floor((left+right)/2); 
            if(obj<this[center]){
                right = center - 1;
            }else{
                left = center + 1;
            }
        }
        return right;
    }
        //测试数据
        var tempArray = new Array('0','10','20','30');
        var obj = 18;
        console(tempArray.binarySearch(obj));
});