JavaScript arrays are several ways to re-common

I was recently interviewed an array to re-do a headache, now specifically to say for everyone to use several methods:

First, the use ES6 Set deduplication (ES6 most commonly used)

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", {}, {}]

Do not consider the compatibility of this method code to the minimum weight.

Second, for use for nesting, and then to re-splice (most commonly used in the ES5)

function UNIQUE (ARR) {            
         for ( var I = 0; I <arr.length; I ++ ) {
             for ( var J = I +. 1; J <arr.length; J ++ ) {
                 IF (ARR [I] == ARR [ J]) {          // first equivalent to a second, splice delete the second method 
                    arr.splice (J,. 1 ); 
                    J - ; 
                } 
            } 
        } 
return ARR; 
} 
var ARR = [1,1, ' to true ',' to true ', to true , to true , 15, 15, to false , to false, Undefined, undefined, null , null , NaN3, NaN3, 'NaN3', 0, 0, 'A', 'A' , {}, {}]; 
    the console.log (UNIQUE (ARR)) 
    // [. 1, "true", 15, false, undefined, NaN, NaN, "NaN", "a", {...}, {...}] // NaN {} and not to heavy, two null directly disappear

Double loop, the outer loop element, the inner loop when the comparison value. Values ​​are the same, this value is omitted.

Third, the use includes (ES6 Method)

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 检测数组是否有某个值
                    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", {…}, {…}]     //{}没有去重

Fourth, the use 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、{}没有去重

Using sort () sorting method, and then traversing the element ratio according to a result of adjacent sorted.

 

Fifth, the use of filter

function UNIQUE (ARR) {
   return arr.filter ( function (Item, index, ARR) {
     // the current element, the first index in the original array == current index value, otherwise the current element 
    return arr.indexOf (Item , 0) === index; 
  }); 
} 
    var ARR = [1,1, 'to true', 'to true', to true , to true , 15, 15, to false , to false , undefined, undefined, null , null , NaN3, NaN3, 'NaN3', 0, 0, 'A', 'A' , {}, {}]; 
        the console.log (UNIQUE (ARR)) 
// [. 1, "to true", to true, 15, to false, undefined , null, "NaN", 0 , "a", {...}, {...}]