Es6: iterator

Iterator

Iterator yes ES6 A new traversal mechanism is introduced , Iterators have two core concepts ：

• Iterators are a unified interface , Its function is to make all kinds of data structures easily accessible , It's through a key for Symbol.iterator To achieve this .
• Iterators are pointers used to traverse data structure elements （ Such as cursor in database ）.

iterative process

1. adopt Symbol.iterator Create an iterator , Point to the start of the current data structure
2. Subsequently passed next Method iterates down to the next location , next Method returns the object in the current location , The object contains value and done Two attributes , value Is the value of the current property , done Used to determine whether traversal ends
3. When done by true The traversal ends

Examples show

      const items=[1,3,4,6,8,9];      
      const ss=items[Symbol.iterator]();      
      let a1=ss.next();      
      console.log(a1);

Iterative data structures

Array、String、Map、Set

for ...of loop

【1】Array

      const items=[1,3,4,6,8,9];      
      for(let item of items){
              
      console.log(item);      
      }

【2】String

      const items="stringforsomething"      
      for(let item of items){
              
      console.log(item);      
      }

【3】Map
Traverse key and value

let maps=new Map(); 
maps.set(0,"hello"); 
maps.set(1,"hello1"); 
maps.set(2,"hello2"); 
maps.set(3,"hello3"); 
for(let [key,value] of maps){
         
	console.log(key+"="+value); 
}

let maps=new Map(); 
maps.set(0,"hello"); 
maps.set(1,"hello1"); 
maps.set(2,"hello2"); 
maps.set(3,"hello3"); 
for(let [key,value] of maps.entries()){
         
	console.log(key+"="+value); 
}

Just traverse key

 let maps=new Map();
  maps.set(0,"hello"); 
  maps.set(1,"hello1"); 
  maps.set(2,"hello2"); 
  maps.set(3,"hello3"); 
  for(let key of maps.keys()){
         
  	console.log(key); 
  }

Just traverse value

 let maps=new Map();
  maps.set(0,"hello");
   maps.set(1,"hello1");
    maps.set(2,"hello2"); 
    maps.set(3,"hello3"); 
    for(let value of maps.values()){
         
  	  console.log(value); 
    }

【4】Set
Traverse the whole set

let sets=new Set();
sets.add(12);
sets.add('hello');
sets.add('hello2');
sets.add('hello3');
sets.add('hello4');
for(let item of sets){
        
	console.log(item);
}

Just traverse key

let sets=new Set();
sets.add(12);
sets.add('hello');
sets.add('hello2');
sets.add('hello3');
sets.add('hello4');
for(let key of sets.keys()){
        
	console.log(key);
}

Just traverse value

let sets=new Set();
sets.add(12);
sets.add('hello');
sets.add('hello2');
sets.add('hello3');
sets.add('hello4');
for(let value of sets.values()){
       
 console.log(value);
 }

Traverse key and value

let sets=new Set();
sets.add(12);
sets.add('hello');
sets.add('hello2');
sets.add('hello3');
sets.add('hello4');
for(let [key,value] of sets.entries()){
        
	console.log(key,value);
}

Iteration of normal objects

 const arrayLink = {
    length: 3, 0: "zero", 1: "one",2:"hello"}
 for(let item of Array.from(arrayLink)){
        
 	console.log(item);
 }