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JS collection

2022-07-25 10:45:00 【PBitW】

List of articles

aggregate
Collection encapsulation
Ensemble method
- Method realization
Assembly room operation
Dictionaries

aggregate

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Collection encapsulation

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In fact, the rookie just saw this , I thought it was a subset problem in my interview question , It turns out that it's not ！

Ensemble method

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Method realization

The way to implement collections here is Object, I think the video is a little too simple , Make the rookie feel I don't know the reason , Maybe it's originally very simple ！

Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title> aggregate </title>
</head>
<body>
  <script>
    function Set(){
    
      //  attribute 
      this.items = {
    };
      //  Method 
      // add Method 
      Set.prototype.add = function(value){
    
        //  Determine whether the current set contains this element 
        if(this.has(value)){
    
          return false;
        }
        //  Add elements to the collection  --> value At the same time as key and value
        this.items[value] = value;
        return true;
      }
      // remove Method 
      Set.prototype.remove = function(value){
    
        //  Determine whether the current set contains this element 
        if(!this.has(value)){
    
          return false;
        }
        //  Delete object key The way to 
        delete this.items[value];
        return true;
      }
      // has Method 
      Set.prototype.has = function(value){
    
        // key and value equally  --> hasOwnProperty Detect whether a property is an object  ** own property **
        return this.items.hasOwnProperty(value);
      }
      // clear Method 
      Set.prototype.clear = function(){
    
        this.items = {
    };
      }
      // size Method 
      Set.prototype.size = function(){
    
        // Object.keys()  Method returns an array of enumerable properties of a given object , The order of the attribute names in the array is consistent with the order returned when the object is traversed in a normal loop 
        return Object.keys(this.items).length;
      }
      // values Method 
      Set.prototype.values = function(){
    
        return Object.keys(this.items);
      }
    }
  </script>
</body>
</html>

Rookie feels after adding notes , It seems much better ！

Be careful ：

Rookie discovery , there values Results returned by method alert The order of coming out is not quite right ！

It should have gone through some sort of sorting ！ The default is this sort , Even if you traverse normally, it is in this order ！

MDN The same is true of the official website ：

thank ：Object.keys(…) The order of object properties ？

Assembly room operation

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Combine

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Code

//  Combine 
Set.prototype.union = function(otherSet){
    
   //this: A collection of objects A otherSet: A collection of objects B
   // 1. Create a new collection 
   let unionset = new Set();

   // 2. take A All elements in the set are added to the new set 
   let values = this.values();
   for(let i = 0;i < values.length;i++){
    
     unionset.add(values[i]);
   }

   // 3  Take out B The elements in the collection --> Add to new collection (add The method has made de judgment )
   values = otherSet.values();
   for(let i = 0;i < values.length;i++){
    
     unionset.add(values[i]);
   }
   return unionset;
 }

intersection

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Code

//  intersection 
Set.prototype.intersection = function(otherSet){
    
  let intersectionSet = new Set();
  //  Judge this The value in ,otherSet Is there any , Add new ones if you have Set
  let values = this.values();
  for(let i = 0; i < values.length;i++){
    
    let item = values[i];
    if(otherSet.has(item)){
    
      intersectionSet.add(item);
    }
  }

  return intersectionSet;
}

Difference set

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Code

//  Difference set 
Set.prototype.difference = function(otherSet){
    
   let differenceSet = new Set();
   let values = this.values();
   //  Judge this Whether the value in is not othersSet Inside , Add a new collection when you're not there 
   for(let i = 0;i < values.length;i++){
    
     let item = values[i];
     if(!otherSet.has(item)){
    
       differenceSet.add(item);
     }
   }
   return differenceSet;
 }

A subset of

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Although this idea still needs to be divided into situations , But really write code , Yes, it is Just cycle and judge That's it ！ Because if the length is greater than otherSet, Then there must be some elements out otherSet Inside ！

//  A subset of 
Set.prototype.subset = function(otherSet){
    
  // 1. Traverse this The elements in , If this There is otherSet There is no such thing as , return false
  let values = this.values();
  for(let i = 0;i < values.length;i++){
    
    let item = values[i];
    if(!otherSet.has(item)){
    
      return false;
    }
  }
  return true;
}

Dictionaries

There is no code in the video here , The reason is that if you use object encapsulation, it is much like a collection , The most commonly used is to use hash table encapsulation , But I didn't learn hash table , Now let's understand , Later, I will learn the hash table to realize ！
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See more directly codewhy The teacher's simple book ：https://www.jianshu.com/p/c53460c9c8e4