What are the 5 ways to deduplicate arrays in JavaScript?

5 ways to remove duplicates from arrays: 1. Use the "[...new Set(arr)]" statement to remove duplicates; 2. Use the "Array.from(new Set(arr))" statement to remove duplicates. Duplication; 3. Use indexOf() to remove duplication; 4. Use includes() to remove duplication; 5. Use filter() to remove duplication.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

How to remove duplicates from an array

1.[...new Set(arr)]

const arr = [1, 2, 3, 2, 3];
[...new Set(arr)]; // [1, 2, 3]

Here is the Set object converted into an array through the expansion syntax of ES6;

2, Array.from(new Set(arr))

const arr = [1, 2, 3, 2, 3];
Array.from(new Set(arr)); // [1, 2, 3]

Due to The elements in Set are unique, whether they are original values ​​or object references, so deduplication can be achieved by converting the array into a Set object.

The Array.from method can convert the Set object into an array

3. Use indexOf to remove duplicates

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、{}没有去重

Create a new empty result array, for loop the original array, determine whether the current element exists in the result array, and skip if there are the same values. , if not the same, push into the array.

4. Use 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 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

5. Use filter

function unique(arr) {
  return arr.filter(function(item, index, arr) {
    //当前元素，在原始数组中的第一个索引==当前索引值，否则返回当前元素
    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", {…}, {…}]

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