摘要：一利用去重中最常用二利用嵌套，然后去重中最常用第一個等同于第二個，方法刪除第二個和沒有去重，兩個直接消失了三利用去重沒有去重四利用沒有去重五利用對象的屬性不能相同的特點進行去重兩個直接去掉了，和去重六利用檢測數組是否有某個值沒有去重

一、利用ES6 Set去重（ES6中最常用）

function unique (arr) {
  return Array.from(new Set(arr))
}
var arr = [1,1,"true","true",true,true,15,15,false,false, undefined,undefined, null,null, NaN, NaN,"NaN", 0, 0, "a", "a",{},{}];
console.log(unique(arr))
//[1, "true", true, 15, false, undefined, null, NaN, "NaN", 0, "a", {}, {}]

二、利用for嵌套for，然后splice去重（ES5中最常用）

function unique(arr){            
    for(var i=0; i
三、利用indexOf去重
function unique(arr) {
    if (!Array.isArray(arr)) {
        console.log("type error!")
        return
    }
    var array = [];
    for (var i = 0; i < arr.length; i++) {
        if (array .indexOf(arr[i]) === -1) {
            array .push(arr[i])
        }
    }
    return array;
}
var arr = [1,1,"true","true",true,true,15,15,false,false, undefined,undefined, null,null, NaN, NaN,"NaN", 0, 0, "a", "a",{},{}];
console.log(unique(arr))
// [1, "true", true, 15, false, undefined, null, NaN, NaN, "NaN", 0, "a", {…}, {…}]  //NaN、{}沒有去重 

四、利用sort()
function unique(arr) {
    if (!Array.isArray(arr)) {
        console.log("type error!")
        return;
    }
    arr = arr.sort()
    var arrry= [arr[0]];
    for (var i = 1; i < arr.length; i++) {
        if (arr[i] !== arr[i-1]) {
            arrry.push(arr[i]);
        }
    }
    return arrry;
}
var arr = [1,1,"true","true",true,true,15,15,false,false, undefined,undefined, null,null, NaN, NaN,"NaN", 0, 0, "a", "a",{},{}];
console.log(unique(arr))
// [0, 1, 15, "NaN", NaN, NaN, {…}, {…}, "a", false, null, true, "true", undefined]      //NaN、{}沒有去重

五、利用對象的屬性不能相同的特點進行去重
function unique(arr) {
    if (!Array.isArray(arr)) {
        console.log("type error!")
        return
    }
    var arrry= [];
     var  obj = {};
    for (var i = 0; i < arr.length; i++) {
        if (!obj[arr[i]]) {
            arrry.push(arr[i])
            obj[arr[i]] = 1
        } else {
            obj[arr[i]]++
        }
    }
    return arrry;
}
var arr = [1,1,"true","true",true,true,15,15,false,false, undefined,undefined, null,null, NaN, NaN,"NaN", 0, 0, "a", "a",{},{}];
console.log(unique(arr))
//[1, "true", 15, false, undefined, null, NaN, 0, "a", {…}]    //兩個true直接去掉了，NaN和{}去重

六、利用includes
function unique(arr) {
    if (!Array.isArray(arr)) {
        console.log("type error!")
        return
    }
    var array =[];
    for(var i = 0; i < arr.length; i++) {
            if( !array.includes( arr[i]) ) {//includes 檢測數組是否有某個值
                    array.push(arr[i]);
              }
    }
    return array
}
var arr = [1,1,"true","true",true,true,15,15,false,false, undefined,undefined, null,null, NaN, NaN,"NaN", 0, 0, "a", "a",{},{}];
console.log(unique(arr))
//[1, "true", true, 15, false, undefined, null, NaN, "NaN", 0, "a", {…}, {…}]     //{}沒有去重

七、利用hasOwnProperty
function unique(arr) {
    var obj = {};
    return arr.filter(function(item, index, arr){
        return obj.hasOwnProperty(typeof item + item) ? false : (obj[typeof item + item] = true)
    })
}
var arr = [1,1,"true","true",true,true,15,15,false,false, undefined,undefined, null,null, NaN, NaN,"NaN", 0, 0, "a", "a",{},{}];
console.log(unique(arr))
//[1, "true", true, 15, false, undefined, null, NaN, "NaN", 0, "a", {…}]   //所有的都去重了

八、利用filter
function unique(arr) {
  return arr.filter(function(item, index, arr) {
    //當前元素，在原始數組中的第一個索引==當前索引值，否則返回當前元素
    return arr.indexOf(item, 0) === index;
  });
}
var arr = [1,1,"true","true",true,true,15,15,false,false, undefined,undefined, null,null, NaN, NaN,"NaN", 0, 0, "a", "a",{},{}];
console.log(unique(arr))
//[1, "true", true, 15, false, undefined, null, "NaN", 0, "a", {…}, {…}]

九、利用遞歸去重
function unique(arr) {
        var array= arr;
        var len = array.length;

    array.sort(function(a,b){   //排序后更加方便去重
        return a - b;
    })

    function loop(index){
        if(index >= 1){
            if(array[index] === array[index-1]){
                array.splice(index,1);
            }
            loop(index - 1);    //遞歸loop，然后數組去重
        }
    }
    loop(len-1);
    return array;
}
var arr = [1,1,"true","true",true,true,15,15,false,false, undefined,undefined, null,null, NaN, NaN,"NaN", 0, 0, "a", "a",{},{}];
console.log(unique(arr))
//[1, "a", "true", true, 15, false, 1, {…}, null, NaN, NaN, "NaN", 0, "a", {…}, undefined]

十、利用Map數據結構去重
function arrayNonRepeatfy(arr) {
  let map = new Map();
  let array = new Array();  // 數組用于返回結果
  for (let i = 0; i < arr.length; i++) {
    if(map .has(arr[i])) {  // 如果有該key值
      map .set(arr[i], true); 
    } else { 
      map .set(arr[i], false);   // 如果沒有該key值
      array .push(arr[i]);
    }
  } 
  return array ;
}
var arr = [1,1,"true","true",true,true,15,15,false,false, undefined,undefined, null,null, NaN, NaN,"NaN", 0, 0, "a", "a",{},{}];
console.log(unique(arr))
//[1, "a", "true", true, 15, false, 1, {…}, null, NaN, NaN, "NaN", 0, "a", {…}, undefined]

十一、利用reduce+includes
function unique(arr){
    return arr.reduce((prev,cur) => prev.includes(cur) ? prev : [...prev,cur],[]);
}
var arr = [1,1,"true","true",true,true,15,15,false,false, undefined,undefined, null,null, NaN, NaN,"NaN", 0, 0, "a", "a",{},{}];
console.log(unique(arr));
// [1, "true", true, 15, false, undefined, null, NaN, "NaN", 0, "a", {…}, {…}]

十二、[…new Set(arr)]
[...new Set(arr)] 
//代碼就是這么少----（其實，嚴格來說并不算是一種，相對于第一種方法來說只是簡化了代碼）