前端日常开发常用功能系列之数组去重

这是前端日常开发常用功能这个系列文章的第一篇，该系列是日常开发中一些常用的功能的再总结、再提炼，以防止遗忘，便于日后复习。该系列预计包含以下内容： 防抖、节流、去重、拷贝、最值、扁平、偏函数、柯里、惰性函数、递归、乱序、排序、注入、上传、下载、截图。。。

本文所记录的数组去重方法只针对一维数组，且数组项都是基本数据类型值

方法一： 二重循环比较去重(因为使用的是‘===’比较，适合数组项为数值、字符串的数组)

const unique1 = arr => {
        const tempArr = arr.concat();
        for(let i = 0; i < tempArr.length; i++) {
            for(let j = i + 1; j < tempArr.length; j++) {
                if(tempArr[i] === tempArr[j]){
                    tempArr.splice(j, 1);
                    j--;
                }
            }
        }
        return tempArr;
    };

方法二： 使用indexOf返回查找元素首次出现位置的特性

const unique2 = arr => {
        const tempArr = arr.concat();
        for(let i = 0; i < tempArr.length; i++) {
            if(tempArr.indexOf(tempArr[i]) !== i) {
                tempArr.splice(i, 1);
                i--;
            }
        }
        return tempArr;
    };

方法三： 使用数组的filter方法

const unique3 = arr => {
        const tempArr = arr.concat();
        return tempArr.filter((item, index, self) => {
            return self.indexOf(item) === index;
        });
    };

方法四：利用对象键特性（该方法不能区分类似这样的数组项 1 和 ‘1’）

const unique4 = arr => {
        const tempArr = arr.concat();
        const tempObj = {};
        for(let i = 0; i< tempArr.length; i++) {
            if(!tempObj[tempArr[i]]) {
                tempObj[tempArr[i]] = true;
            } else {
                tempArr.splice(i, 1);
                i--;
            }
        }
        return tempArr;
    };

方法五：利用es6 set数据结构的特性

const unique5 = arr => {
        return Array.from(new Set(arr));
    };

方法六： 利用数组原型的includes方法

const unique6 = arr => {
        const tempArr = [];
        for(let i = 0; i < arr.length; i++) {
            if(!tempArr.includes(arr[i])) {
                tempArr.push(arr[i]);
            }
        }
        return tempArr;
    };

不妨简单测试一下这几种方法的性能，使用一个较大的数组

const ar =  [1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3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,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6,7,4,1,1,2,3,5,3,1,5,6];
    console.time('test1');
    let temp1 = unique1(ar);
    console.timeEnd('test1');

    console.time('test2');
    let temp2 = unique1(ar);
    console.timeEnd('test2');

    console.time('test3');
    let temp3 = unique1(ar);
    console.timeEnd('test3');

    console.time('test4');
    let temp4 = unique1(ar);
    console.timeEnd('test4');

    console.time('test5');
    let temp5 = unique1(ar);
    console.timeEnd('test5');

    console.time('test6');
    let temp6 = unique1(ar);
    console.timeEnd('test6');
    
    console.log(temp1, temp2, temp3, temp4, temp5, temp6);

测试结果大概如下

可以看到这6种方法都得到了正确的结果

方法1使用了双重循环，不出意料的相对较慢

但同时注意到splice的性能似乎并不好。。。