Question

JS判断数组中是否有重复值得三种实用方法

Answer 1

//先排序，相邻两个元素相同即为重复
            Array.prototype.isRepeat1 = function() {
                this.sort();
                var result = [this[0]];
                for (var i = 1; i < this.length; i++) {
                    if (this[i] == result[result.length - 1]) {
                        return true;
                    }
                }
                return false;
            };
            
            //循环，把元素放入map中，如果在map中能找到就说明重复
            Array.prototype.isRepeat2 = function() {
                var map = {}, result = [];
                for (var i = 0; i < this.length; i++) {
                    if (map[this[i]]) {
                        return true;
                    }
                    map[this[i]] = true;
                }
                return false;
            };
            
            //用indexOf/lastIndexOf返回的位置比较判断是否重复
            Array.prototype.isRepeat3 = function() {
                for (var i = 0; i < this.length; i++) {
                    if (this.indexOf(this[i]) != i){
                        return true;
                    }
                }
                return false;
            };