数组去重

1 双重for循环

function distinct(value) {
        let arr = value;
        for (let i=0, len=arr.length; i<len; i++) {
            for (let j=i+1; j<len; j++) {
                if (arr[i] == arr[j]) {
                    arr.splice(j, 1);
                    // splice 会改变数组长度，所以要将数组长度 len 和下标 j 减一
                    len--;
                    j--;
                }
            }
        }
        return arr
    }
    var arrlist = [1, 3, 5, 3, 5, 6, 7]
    var dealArr = distinct(arrlist)
    console.log(dealArr)  // 此性能最差   

2  Array.filter() + indexOf

 function distinct(value) {
      let arr = value;
      return arr.filter((item, index)=> {
        return arr.indexOf(item) === index
      })
    }
    var arrlist = ['ab', 'cd', 'ab', 6, 5, 6, 7]
    var dealArr = distinct(arrlist)
    console.log(dealArr)  // 此性能较差 

3 ES6 Set

var arr = [1, 2, 4, 4, 6, 6, 8]
    let tempArr = new Set(arr)
    let dealArr = Array.from(tempArr)
    console.log(dealArr) // 性能优

4 Array.sort()

 function distinct(value) {
        let arr = value
        arr = arr.sort()
        let result = [arr[0]]

        for (let i=1, len=arr.length; i<len; i++) {
            arr[i] !== arr[i-1] && result.push(arr[i])
        }
        return result
    }
    var arrlist = ['ab', 'cd', 'ab', 6, 5, 6, 7]
    var dealArr = distinct(arrlist)
    console.log(dealArr)  // 此性能比较优秀 

5 for...of + Object

function distinct(value) {  // 利用对象的属性不会重复这一特性，校验数组元素是否重复
        let arr = value
        let result = []
        let obj = {}

        for (let i of arr) {
            if (!obj[i]) {
                result.push(i)
                obj[i] = 1
            }
        }

        return result
    }
    var arrlist = ['ab', 'cd', 'ab', 6, 5, 6, 7]
    var dealArr = distinct(arrlist)
    console.log(dealArr)  // 此性能最优