How to implement array deduplication?

To get rid of duplicate values in an array, the conventional solution uses some of the ARRAY apis of ES5, while a simpler approach uses a combination of the ES6 extension operator and the Set data structure.

Here are four solutions:

1. Method one, use the splice method to remove duplicate elements

function normalize (arr) {
  if (arr && Array.isArray(arr)) {
    var len = arr.length,
        map = {};
    for (var i = len - 1; i >= 0; i--) {
      if (arr[i] in map) {
        arr.splice(i, 1);
      } else {
        map[arr[i]] = true; }}returnarr; }}Copy the code

2. Method two uses indexOf to identify duplicate elements

function normalize (arr) {
  if (arr && Array.isArray(arr)) {
    var len = arr.length,
        res = [];
    for (var i = 0; i < len; i++) {
      if (res.indexOf(arr[i]) == - 1) { res.push(arr[i]); }}returnres; }}Copy the code

3. Method three, skillfully use the extension operator and Set data structure

function normalize (arr) {
  if (arr && Array.isArray(arr)) {
    var res = [...new Set(arr)];
    returnres; }}Copy the code

4. Method 4: Use the new API in ES6 —Array.from()To implement the function of extending the operator in method three

function normalize (arr) {
  if (arr && Array.isArray(arr)) {
    var res = Array.from(new Set(arr));
    returnres; }}Copy the code

The code for the test is as follows:

/* Test code */
var arr = [7.1.'hi'.1.'hi'.true.null.undefined.true.null.undefined];
console.log('Array deduplicated', normalize(arr));
Copy the code