更多语言去重算法：github.com/microwind/a…

JavaScript数组去重的N种方法，总有一种适合你。面试时你可以反问主考官了。

class UniqueArray {
    constructor(arr) {
        this.arr = arr;
    }
    // 1. new array
    unique1() {
        console.time("time");
        var arr = this.arr.slice(0);
        var newArr = [];
        for (var i = 0, l = arr.length; i < l; i++) {
            for (var j = 0; j <= i; j++) {
                if (arr[i] === arr[j]) {
                    if (i === j) {
                        newArr.push(arr[i]);
                    }
                    break;
                }
            }
        }
        console.log("new array result:", newArr);
        console.timeEnd("time");
    }
    unique2() {
        // 2. new array + indexOf
        console.time("time");
        var arr = this.arr.slice(0);
        var newArr = [];
        for (var i = 0, l = arr.length; i < l; i++) {
            if (newArr.indexOf(arr[i]) < 0) {
                newArr.push(arr[i]);
            }
        }
        console.log("new array + indexOf:", newArr);
        console.timeEnd("time");
    }
    unique3() {
        // 3. new array + includes
        console.time("time");
        var arr = this.arr.slice(0);
        var newArr = [];
        for (var i = 0, l = arr.length; i < l; i++) {
            if (!newArr.includes(arr[i])) {
                newArr.push(arr[i]);
            }
        }
        console.log("new array + includes:", newArr);
        console.timeEnd("time");
    }
    unique4() {
        // 4. one array last -> first
        console.time("time");
        var arr = this.arr.slice(0);
        var l = arr.length;
        while (l-- > 0) {
            for (var i = 0; i < l; i++) {
                if (arr[l] === arr[i]) {
                    arr.splice(l, 1);
                    break;
                }
            }
        }
        console.log("one array last -> first result:", arr);
        console.timeEnd("time");
    }
    unique5() {
        // 5. one array last -> first from right
        console.time("time");
        var arr = this.arr.slice(0);
        var l = arr.length;
        var i = 0;
        while (l-- > 0) {
            i = l;
            while (i-- > 0) {
                if (arr[l] === arr[i]) {
                    arr.splice(l, 1);
                    break;
                }
            }
        }
        console.log("one array last -> first from right:", arr);
        console.timeEnd("time");
    }
    unique6() {
        // 6. one array first -> last
        console.time("time");
        var arr = this.arr.slice(0);
        var l = arr.length;
        for (var i = 0; i < l; i++) {
            for (var j = i + 1; j < l; j++) {
                if (arr[i] === arr[j]) {
                    arr.splice(j, 1);
                    l--;
                    i--;
                    break;
                }
            }
        }
        console.log("one array first -> last result:", arr);
        console.timeEnd("time");
    }
    unique7() {
        // 7. forEach + indexOf
        console.time("time");
        var arr = this.arr.slice(0);
        var newArr = [];
        for (var i = 0, l = arr.length; i < l; i++) {
            if (i === arr.indexOf(arr[i])) {
                newArr.push(arr[i]);
            }
            else if (arr.indexOf(arr[i]) >= 0) {
                // break same item
                continue;
            }
        }
        console.log("forEach + indexOf result:", newArr);
        console.timeEnd("time");
    }
    unique8() {
        // 8. filter + indexOf
        console.time("time");
        var arr = this.arr.slice(0);
        console.log("filter + indexOf: ", arr.filter((item, i) => i === arr.indexOf(item)));
        console.timeEnd("time");
    }
    unique9() {
        // 9. Array.from object
        console.time("time");
        var arr = this.arr.slice(0);
        var obj = {};
        arr.forEach((item) => {
            obj[item] = item;
        });
        console.log("Array.from object:", Array.from(Object.values(obj)));
        console.timeEnd("time");
    }
    unique10() {
        // 10. Array.from Map
        console.time("time");
        var arr = this.arr.slice(0);
        var map = new Map();
        arr.forEach((item, i) => {
            map.set(item, item);
        });
        console.log("Array.from Map:", Array.from(map.values()));
        console.timeEnd("time");
    }
    unique11() {
        // 11. from Set
        console.time("time");
        var arr = this.arr.slice(0);
        var set = new Set(arr);
        console.log("from Set:", Array.from(set));
        console.timeEnd("time");
    }
    unique12() {
        // 12. sort+remove
        console.time("time");
        var arr = this.arr.slice(0);
        arr.sort();
        var l = arr.length;
        while (l-- > 1) {
            if (arr[l] === arr[l - 1]) {
                arr.splice(l, 1);
            }
        }
        console.log("sort+remove:", arr);
        console.timeEnd("time");
    }
    unique13() {
        // 13. sort+remove ASE
        console.time("time");
        var arr = this.arr.slice(0);
        arr.sort((a, b) => {
            return a.toString() > b.toString() ? 1 : -1;
        });
        var l = arr.length;
        for (var i = 0; i < l - 1; i++) {
            if (arr[i] === arr[i + 1]) {
                arr.splice(i, 1);
                l--;
                i--;
            }
        }
        console.log("sort+remove ASE:", arr);
        console.timeEnd("time");
    }
    unique14() {
        // 14. from reduce
        console.time("time");
        var arr = this.arr.slice(0);
        var newArr = arr.reduce((result, item) => {
            if (!Array.isArray(result)) {
                result = [result];
            }
            return result.includes(item) ? result : [...result].concat(item);
        });
        console.log("from reduce:", newArr);
        console.timeEnd("time");
    }
    unique15() {
        // 15. indexOf + new Array push
        console.time("time");
        var arr = this.arr.slice(0);
        var newArr = [];
        for (var i = 0, l = arr.length; i < l; i++) {
            var item = arr[i];
            if (newArr.indexOf(item) < 0) {
                newArr.push(item);
            }
        }
        console.log("new Array push:", newArr);
        console.timeEnd("time");
    }
    unique16() {
        // 16. filter+hasOwnProperty
        console.time("time");
        var arr = this.arr.slice(0);
        var obj = {};
        arr = arr.filter((item) => {
            return obj.hasOwnProperty(typeof item + item)
                ? false
                : (obj[typeof item + item] = true);
        });
        console.log("filter+hasOwnProperty:", arr);
        console.timeEnd("time");
    }
    recursionUnique(arr, len) {
        // 17. recursion
        console.time("time");
        if (len <= 1) {
            return arr;
        }
        var l = len;
        var last = l - 1;
        var isRepeat = false;
        while (l-- > 1) {
            if (arr[last] === arr[l - 1]) {
                isRepeat = true;
                break;
            }
        }
        if (isRepeat) {
            arr.splice(last, 1);
        }
        return this.recursionUnique(arr, len - 1);
    }
    recursionUniqueNew(arr, len) {
        // 18. recursionUniqueNew
        console.time("time");
        if (len <= 1) {
            return arr;
        }
        var l = len;
        var last = l - 1;
        var lastItem = arr[last];
        var isRepeat = false;
        var result = [];
        while (l-- > 1) {
            if (lastItem === arr[l - 1]) {
                isRepeat = true;
                break;
            }
        }
        arr.splice(last);
        if (!isRepeat) {
            result.push(lastItem);
        }
        return this.recursionUniqueNew(arr, len - 1).concat(result);
    }
}
(function () {
    var arr = [1, 1, 3, -1, 1, 2, 2, 4, 2, 2, -1];
    const unique = new UniqueArray(arr);
    console.log("begin to test:\n");
    for (var i = 1; i <= 16; i++) {
        unique["unique" + i]();
    }
    console.log("recursionUnique:", unique.recursionUnique(arr.slice(0), arr.length));
    console.timeEnd("time");
    console.log("recursionUniqueNew:", unique.recursionUniqueNew(arr.slice(0), arr.length));
    console.timeEnd("time");
})();
/**
begin to test:

new array result: [ 1, 3, -1, 2, 4 ]
time: 2.387ms
new array + indexOf: [ 1, 3, -1, 2, 4 ]
time: 0.197ms
new array + includes: [ 1, 3, -1, 2, 4 ]
time: 0.209ms
one array last -> first result: [ 1, 3, -1, 2, 4 ]
time: 0.064ms
one array last -> first from right: [ 1, 3, -1, 2, 4 ]
time: 0.054ms
one array first -> last result: [ 1, 3, -1, 2, 4 ]
time: 0.052ms
forEach + indexOf result: [ 1, 3, -1, 2, 4 ]
time: 0.059ms
filter + indexOf:  [ 1, 3, -1, 2, 4 ]
time: 0.076ms
Array.from object: [ 1, 2, 3, 4, -1 ]
time: 0.278ms
Array.from Map: [ 1, 3, -1, 2, 4 ]
time: 0.302ms
from Set: [ 1, 3, -1, 2, 4 ]
time: 0.274ms
sort+remove: [ -1, 1, 2, 3, 4 ]
time: 0.552ms
sort+remove ASE: [ -1, 1, 2, 3, 4 ]
time: 0.114ms
from reduce: [ 1, 3, -1, 2, 4 ]
time: 0.429ms
new Array push: [ 1, 3, -1, 2, 4 ]
time: 0.078ms
filter+hasOwnProperty: [ 1, 3, -1, 2, 4 ]
time: 0.282ms
recursionUnique: [ 1, 3, -1, 2, 4 ]
time: 0.049ms
recursionUniqueNew: [ 1, 3, -1, 2, 4 ]
time: 0.051ms
*/

更多语言去重算法：github.com/microwind/a…