The method of _javascript of JS Array to summarize the skill

Three kinds of methods

Using IndexOf to judge new arrays

Underscore.js is actually used in a similar indexof

 Incoming array
 function unique1 (arr) {
  var tmparr = [];
  for (var i=0 i<arr.length; i++) {
   //If the current array has already been saved in the temporary array, skip,
   //or push the current item to the temporary array if
   (tmparr.indexof (Arr[i]) = = = 1) {
    Tmparr.push (arr[i])
   ;
  }
  return tmparr;
 }

Using indexof to judge old arrays

 function Unique2 (arr) {
  var tmparr = [];//result array for
  (Var i=0; i<arr.length; i++) {
   // If the first occurrence of the current array in the current array is not I,
   //It means that item I is duplicated and ignored. Otherwise deposit the result array
   if (Arr.indexof (arr[i]) = = i) {
    tmparr.push (arr[i]);
   }
  return tmparr;
 }

Use hash to find

This uses the JS object's implementation is the hash table characteristic

 function Unique3 (arr) {
  var tmparr = [], hash = {};//hash to hash table for
  (var i=0;i<arr.length;i++) {
   if (!hash[ Arr[i]] {//If there is no current item
    hash[arr[i] = true;//in hash table
    Tmparr.push (arr[i));//Save temporary Array
   }
  }
  return tmparr;
 }

Array extension

 Array.prototype.unique1 = function () {
  var tmparr = []; 
  for (var i = 0; i < this.length i++) {
   if (Tmparr.indexof (this[i)) = = 1) {
    Tmparr.push (this[i]);
  }
  return tmparr;
 }

 Array.prototype.unique2 = function () {
   var tmparr = [];//result array for
   (var i = 0; i < this.length; i++) {
    if ( This.indexof (this[i]) = = i) {
     tmparr.push (this[i])
    ;
   }
   return tmparr;
 }

 Array.prototype.unique3 = function () {
   var tmparr=[], hash = {};
   for (var i = 0; i < this.length i++) {
    if (!hash[this[i]]) {
      Hash[this[i]] = true; 
      Tmparr.push (This[i]); 
    }
   return tmparr;
 }

Using Set

Set and map are new data structures in ES6
Set can directly store a set of keys that are not duplicated, and this key can also be objects, strings, etc.
Create set

var s = new Set ([1, 2, 3,]);
S Set {1, 2, 3}

New elements

>>> S.add (4)
>>> s
{1, 2, 3, 4}
>>> S.add (4)
>>> s
{1, 2, 3, 4} Duplicate elements are not added

Delete Element

S Set {1, 2, 3, 4}
S.delete (3);
S Set {1, 2, 4}

Traversing elements

Map and set cannot use subscript
The ES6 Standard introduces a new type of iterable, Array, map, and set all belong to the iterable type

var s = new Set ([' A ', ' B ', ' C ']);

for (var x of s) {//Traverse set
  alert (x);
}

or directly using the Iterable built-in foreach method
The Foreach method is introduced by the ES5.1 standard.

var s = new Set ([' A ', ' B ', ' C ']);
S.foreach (function (element, set) {
  alert (element);
});

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