ES6 adds -iterator traversal, for..Of loop

Catalog

One .interator Iterator

1. effect

2. Have iterator The data structure of the interface is as follows :

3.iterator Principle of traverser

4.Iterator The execution mechanism of the traverser

 5. To strengthen

One .for...of loop

                for .. of Realization principle

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One .interator Iterator

1. effect

• For a variety of data structures , Provide a unified , Convenient access interface
• for for...of consumption

2. Have iterator The data structure of the interface is as follows :

• Array/ An array of class
• String
• Set
• Map

3.iterator Principle of traverser

es6 Regulations , default iterator Interface deployed in data structure Symbol.iterator( Unique data type attributes ) attribute , Or say , As long as a data structure has Symbol,iterator attribute , Namely " Ergodic "

4.Iterator The execution mechanism of the traverser

const arr = [ " The tiger "," The tiger "," raw "," Wei " ]

1: Get the iterator object , It is essentially a pointer object

const iter = arr[Symbol.iterator]()

console,log(iter)

2: call next Method , The pointer points to the first member of the data structure . And so on

say concretely , Is to return a containing value and done Objects with two properties .

among ,value Property is the value of the current member ,done Property is a Boolean value , Indicates whether the traversal ends .

console.log(iter.next() )

console.log(iter.next() )

console.log(iter.next() )

console.log(iter.next() )

console.log(iter.next() )

 5. To strengthen

const str = "2022"

const iter = str[Symbol.iterator]()

console.log(iter.next() )

console.log(iter.next() )

console.log(iter.next() )

console.log(iter.next() )

console.log(iter.next() )

const obj = {

a:1, b:2, c:3 } 

obj.[Symbol.iterator]()

There is no deployment on the object Symbol.iterator attribute   

One .for...of loop

A data structure as long as Internally deployed Symbol.iterator attribute , Just It can be used for..of Loop through his members , in other words ,for..of The data structure is called inside the loop Symbol.iterator Method .

for..of The range that a loop can use includes arrays ,Set and Map structure .

Some array like objects ( Such as arguments object ,DOM NodeList object ),Genderator object , And strings .

and es5 Traversing objects for .. in similar

const arr = [" The tiger "," The tiger "," raw "," Wei "] 

for(let item of arr){ console.log(item) }

 const str = "2022"

for(let item of str){ console.log(item) }

 const obj = { a:1 ,b:2, c:3 }

for(let item of obj){ console.log(item) } Report errors reason : Objects cannot be iterated

for .. of Realization principle

const obj = { a:1 ,b:2, c:3 }

obj[Symbol.iterator] = function(){

let i = 0;

const keys = Object.keys(this)

return {

next:()=>{

return i <= keys.length = 1 ? { value:this[keys[i++]] } : {value:undefined, done:true  }  }  }  }

for(let v og obj ){console.log(v)}

const obj = { a:1 ,b:2, c:3 }

obj[Symbol.iterator] = function(){

let i = 0;

const keys = Object.keys(this)

return {

next:()=>{

return i <= keys.length = 1 ? { value:keys[i++] } : {value:undefined, done:true  }  }  }  }

for(let v og obj ){console.log(v)}