JavaScript常用数组去重的方法及对比详解

 const arr = [ 1, 1, "1", "1", 0, 0, "0", "0", true, false, "true", "false", "a", "A", undefined, undefined, "undefined", null, null, 'null', NaN, NaN, +0, -0, new String("1"), new String("1"), Symbol(1), Symbol(1), {}, {}, /a/, /a/, [], [] ];

console.log(1 == "1"); // true
console.log(1 === "1"); // false

console.log(0 == "0"); // true
console.log(0 === "0"); // false

console.log(0 == +0); // true
console.log(0 === +0); // true

console.log(0 == -0); // true
console.log(0 === -0); // true

console.log(+0 == -0); // true
console.log(+0 === -0); // true

console.log(0 == false); // true
console.log(0 === false); // false

console.log(0 == undefined); // false
console.log(0 === undefined); // false

console.log(0 == null); // false
console.log(0 === null); // false

console.log(1 == true); // true
console.log(1 === true); // false

console.log(undefined == null); // true
console.log(undefined === null); // false

console.log(NaN == NaN); // false
console.log(NaN === NaN); // false

console.log(new String("1") == new String("1")); // false
console.log(new String("1") === new String("1")); // false
Object.prototype.toString.call(new String('1')) // '[object String]'


console.log(/a/ == /a/); // false
console.log(/a/ === /a/); // false
Object.prototype.toString.call(/a/); //'[object RegExp]'


console.log(Symbol(1) == Symbol(1)); // false
console.log(Symbol(1) === Symbol(1)); // false

console.log({} == {}); // false
console.log({} === {}); // false

console.log([] == []); // false
console.log([] === []); // false

// 暴力解法一

function unique(array) {
    if (!Array.isArray(array)) {
      console.log("type error!");
      return;
    }
    const res = [array[0]];
    let arrLen = array.length;
    let resLen = res.length;
    
    for (let i = 0; i < arrLen; i++) {
      let flag = true;
      for (let j = 0; j < resLen; j++) {
        if (array[i] === res[j]) {
          flag = false;
          break;
        }
      }
      if (flag) {
        res.push(array[i]);
        resLen = res.length;
      }
    }
    return res;
}
// [1, '1', 0, '0', true, false, 'true', 'false', 'a', 'A', undefined, 'undefined', null, 'null', NaN, NaN, String {'1'}, String {'1'}, Symbol(1), Symbol(1), {}, {}, /a/, /a/, [], []]

// ES6 Array.from + Set 方法一
function unique(array) {
    if (!Array.isArray(array)) {
      console.log('type error!')
      return
    }
    return Array.from(new Set(array))
}

// ES6 点运算 + Set 方法二
function unique1(array) {
    if (!Array.isArray(array)) {
      console.log('type error!')
      return
    }
    return [...new Set(arr)]
}

// ES6 箭头函数 + 点运算 + Set 方法三
const unique2 = (array) => {
    if (!Array.isArray(array)) {
      console.log('type error!')
      return
    }
    return [...new Set(arr)]
}

// ES6 Map + ES5 filter  方法四
function unique3(array) {
    if (!Array.isArray(array)) {
      console.log('type error!')
      return
    }
    const seen = new Map()
    return array.filter((a) => !seen.has(a) && seen.set(a, 1))
}

// indexOf + forEach 利用indexOf检测元素在新数组是否存在
function unique(array) {
    if (!Array.isArray(array)) {
        console.log('type error!')
        return
    }
    const newArr = [];
    array.forEach((el) => {
      if (newArr.indexOf(el) === -1) {
        newArr.push(el);
      }
    });
    return newArr;
}

// indexOf + forEach 利用indexOf检测元素在新数组是否存在
function unique(array) {
    if (!Array.isArray(array)) {
        console.log('type error!')
        return
    }
    return array.filter((item, index) => {
        return array.indexOf(item) === index;
    });
}

console.log([NaN].indexOf(NaN)); // -1

console.log([NaN].indexOf(NaN)); // -1

// sort()方法不支持Symbol，Symbol不支持转换成字符串
function unique(array) {
    if (!Array.isArray(array)) {
      console.log("type error!");
      return;
    }
    const sortArr = array.sort();
    const newArr = [];
    sortArr.forEach((el, i) => {
      if (sortArr[i] !== sortArr[i - 1]) {
        newArr.push(el);
      }
    });
    return newArr;
}

// 利用includes()方法检查新数组是否包含原数组的每一项
function unique(array) {
    if (!Array.isArray(array)) {
      console.log("type error!");
      return;
    }
    
    const newArr = [];
    array.forEach((el) => {
      newArr.includes(el) ? newArr : newArr.push(el);
    });
    return newArr;
}

// 利用includes()方法检查新数组是否包含原数组的每一项
function unique(array) {
    if (!Array.isArray(array)) {
      console.log("type error!");
      return;
    }
    
    return array.reduce((pre, cur) => {
      !pre.includes(cur) && pre.push(cur);
      return pre;
    }, []);
}

// 利用了对象的key不可以重复的特性来进行去重
function unique(array) {
    if (!Array.isArray(array)) {
      console.log("type error!");
      return;
    }
    
    const obj = {};
    const newArr = [];
    array.forEach((val) => {
      if (!obj[typeof val + JSON.stringify(val)]) {
        // 将对象序列化之后作为key来使用
        obj[typeof val + jsON.stringify(val)] = 1;
        newArr.push(val);
      }
    });
    return newArr;
}