How to remove duplicates from front-end html array

This article mainly introduces the method of deduplicating front-end html arrays. It has certain reference value. Now I share it with you. Friends in need can refer to it

Array deduplication

Knowledge points used:

1:indexOf()

This method returns the index value of the first occurrence of element in the array;

If there is, the index value will be returned normally;

If the retrieved content does not exist in the array , then return -1

2: for loop

Exercise: Array deduplication

//The first method

##

var aList = [1,2,3,4,4,3,2,1,2,3,4,5,6,5,5,3,3,4,2,1];
var aList2 = [];
for (var i = 0 ; i < aList.length ; i ++) {
　　var value = aList[i]
　　if (aList.indexOf(value) + 1) {
　　　　console.log(&#39;重复了&#39;，value)
　　} else {
　　　　aList2.push(value)
　　}　　　　　　　　
　　}
　　console.log(aList2)

// 第二种方法
var aList = [1,2,3,4,4,3,2,1,2,3,4,5,6,5,5,3,3,4,2,1];
for(var i=0;i<aList.length;i++)
{
   if(aList.indexOf(aList[i])==i)
   {
       　　aList2.push(aList[i]);
   }
}
alert(aList2);

// 第三种方法
var aList = [1,2,3,4,4,3,2,1,2,3,4,5,6,5,5,3,3,4,2,1];
  for (var i = 0; i < aList.length; i++) {
           　　var item = aList[i]
           if (newArray.indexOf(item) == -1) {
               　　newArray.push(item)
           } else {
               　　console.log(&#39;重复了&#39;,item)
           }
       }

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