js实现数组去重的几种方法

//1、set方法去重，Array.from转化为数组
var a=[1,2,3,3,2,1,4,4]
var b = new Set(a)
b = Array.from(b)
console.log('b',b)

//2、set方法去重，展开元素赋值[...arr]
var a = [2,4,4,5,5,3,33,3,3,3]
var b = new Set(a)
b= [...b]
console.log('b',b)

//3、双重for循环
var a = [1,2,1,2,4,5,6,3,3,5]
var res = unique(a)
function unique(a) {

for(var i=0;i<a.length;i++){
    for(var j=i+1;j<a.length;j++){
        if(a[i] == a[j]){
            a.splice(j,1)
            j--
        }
    }
}
return a

}
console.log(res)

// 4、利用indexOf去重 + for循环
var array = []
for(var i = 0;i<arr.length;i++) {

if(array.indexOf(arr[i])=== -1){
    array.push(arr[i])
}

}
console.log('res',array)

5、利用filter()去重 + indexOf
var arr = [3,3,44,21,22,21,12]
var newArr = arr.filter((item,index)=>{

return arr.indexOf(item) === index  //因为indexOf 只能查找到第一个

})
console.log('newArr',newArr)

6、利用sort去重
var arr = [2,2,3,2,3,4,5,6,5]
arr.sort = arr.sort()
var a = [arr[0]]
for(var i= 1;i<arr.length;i++){

if(arr[i]!==arr[i-1]){
    a.push(arr[i])
}

}
console.log('a',a)

//7、利用includes实现数组去重
var arr= [1,1,22,2,23,33,333,223,2311,1,2,2,22,2]
var newArr = []
for(var i=0;i<arr.length;i++){

if(!newArr.includes(arr[i])){
    newArr.push(arr[i])
}

}
console.log(newArr)