js数组中判断是否有重复项

1. 方法一

   let s = ary.join(",")+",";
   for(let i=0;i<ary.length;i++) {
       if(s.replace(ary[i]+",","").indexOf(ary[i]+",")>-1) {
           alert("数组中有重复元素：" + ary[i]);
           break;
       }
   }        

2. 方法二

   let  ary = new Array("111","22","33","111");
   let nary=ary.slice().sort();
   for(let i=0;i<ary.length;i++){
       if (nary[i]==nary[i+1]){
           alert("数组重复内容："+nary[i]);
       }
   }    

    

3. 方法三

   function isRepeat(arr){
       let  hash = {};
       for(let i in arr) {
           if(hash[arr[i]]) {
               return true;
   　　     }
           hash[arr[i]] = true;
       }
       return false;
   }