It seems that it is not the most complete array de duplication method

1. The simplest and rudest way, double for loop

let arr = [9, 5, 6, 5, '1', '1', true, 5, true]; for (var i = 0; i < arr.length; i++) { for (var j = i + 1; j < arr.length; j++) { if(arr[i] === arr[j]){ arr.splice(j,1); } } } console.log(arr); // [9, 5, 6, "1", true, undefined, null, NaN, NaN, {...}, {...}] // Two NaN, because NaN!=NaN

2.indexOf

let a = []; for (var i = 0; i < arr.length; i++) { if(a.indexOf(arr[i]) === -1){ a.push(arr[i]); } } console.log(a); // [9, 5, 6, "1", true, undefined, null, NaN, NaN, {...}, {...}] // Two NaN, because NaN!=NaN

3.includes

for (var i = 0; i < arr.length; i++) { if(!a.includes(arr[i])){ a.push(arr[i]); } } console.log(a); // [9, 5, 6, "1", true, undefined, null, NaN, {...}, {...}]

4.Set

let a = [...(new Set(arr))]; console.log(a); // [9, 5, 6, "1", true, undefined, null, NaN, {...}, {...}]

5.filter

let a = arr.filter(function(value, index){ return arr.indexOf(value, 0) === index; }) console.log(a);// [9, 5, 6, "1", true, undefined, null, {...}, {...}] arr.filter(function(value){ return a.indexOf(value) === -1 ? a.push(value) : a; }) console.log(a);// [9, 5, 6, "1", true, undefined, null, NaN, NaN, {...}, {...}]

6.sort

arr = arr.sort(); // Sort, if they are the same, they will be next to each other a.push(arr[0]); // Put the first element of the array first for (var i = 1; i < arr.length; i++) { if(arr[i] !== arr[i - 1]){ a.push(arr[i]); } }

7.reduce

arr = arr.sort(); arr.reduce(function(preVal, nowVal){ if(preVal !== nowVal){ a.push(preVal); } return nowVal; }, a) arr.reduce(function(preVal, nowVal){ return a.indexOf(nowVal) === -1 ? a.push(nowVal) : a; }, a) console.log(a); //["1", 5, 6, 9, NaN, NaN, {...}, {...}, null, true, undefined]

8.hasOwnProperty

let obj = {}; for (var i = 0; i < arr.length; i++) { if(!obj.hasOwnProperty(obj[typeof arr[i] + arr[i]])){ obj[typeof arr[i] + arr[i]] = arr[i]; } } console.log(Object.values(obj)); //[9, 5, 6, "1", true, undefined, null, NaN, {… }]Unable to judge object

9. Object array de duplication method

let obj = {}; for (var i = 0; i < arr.length; i++) { if(!obj[typeof arr[i] + arr[i]]){ obj[typeof arr[i] + arr[i]] = arr[i]; } } console.log(Object.values(obj)); //[9, 5, 6, "1", true, undefined, null, NaN, {...}]

10.Map

let map = new Map(); for (var i = 0; i < arr.length; i++) { if(!map.get(arr[i])){ map.set(arr[i], arr[i]); } } console.log(map);

• supplement

I want to talk about forEach and map

arr.forEach( function(element, index) { console.log(element); }); arr.map(function(element, index){ console.log(element); });

• Same points

  • They are all used to traverse arrays.

• Difference

  • map can have return value, forEach has no return value.

  let arr = [9,3,6,3,6,3]; arr = arr.forEach( function(element, index) { return element + 1; }); console.log(arr); // undefined arr = arr.map(function(element, index){ return element + 1; }); console.log(arr); //[10, 4, 7, 4, 7, 4]

  • forEach can't interrupt halfway

  let arr = [9,3,6,3,6,3]; arr.forEach( function(element, index) { console.log(element); if(index === 2){ return; //It's useless. break,continue will report an error. It's invalid } });

• forEach Simulation Implementation

  Array.prototype.bforEach = function (fn) { let array = this; for (var i = 0; i < array.length; i++) { fn(array[i], i, array); } } arr.bforEach(function(element, index){ console.log(element); // 9, 3, 6, 3, 6, 3 });

• map simulation implementation

  Array.prototype.Map = function (fn) { let array = this, a = [], r; for (var i = 0; i < array.length; i++) { r = fn(array[i], i, array); a.push(r); } return a; }

  Like can point a like, or pay attention to. Encourage a self-taught front-end college student.

3 December 2019, 07:38 | Views: 1580