New features of ES6

Preface

Now in the mainstream front-end framework ,Vue.js etc. , Will be used ES6 New features
Still have java Basic learning is very simple

let and const

• let, prevent var The defined variable becomes a global variable

• const, Be similar to java Medium final keyword , Cannot be modified

String extension

• includes() Returns a Boolean value , Is the parameter string found
• startsWith() Returns a Boolean value , Whether the parameter string is at the head of the original string （ Whether or not to xxx start ）
• endsWith() Returns a Boolean value , Whether the parameter string is at the end of the original string ( Whether it ends with xxx)

String template `` Number pad one left

Structure expression

ES6 Allows you to extract values from arrays and objects according to certain patterns , And then assign values to variables , This is called deconstruction

An array of deconstruction

Object to deconstruct

Function optimization

Function parameter defaults

Arrow function

map

Receive a function , All elements in the original array are processed with this function and put into the new array to return

reduce

reduce()∶ Receive a function ( must ) And an initial value （ Optional ) This function takes two arguments ∶

• The first parameter is the last time reduce Results of processing
• The second parameter is the next element in the array to be processed

reduce() The elements in the array will be used from left to right with reduce Handle , And treat the result as next time reduce The first parameter of . If it's the first time , The first two elements are taken as calculation parameters , Or take the initial value specified by the user as the starting parameter

give an example

Extension operator

…, Convert an array to a comma separated sequence of parameters

Promise

the i Predicate Promise, It's simply a container , It holds an event that will end in the future （ This is usually an asynchronous operation ） Result . grammatically ,Promise It's an object , From it you can get messages for asynchronous operations .Promise Provide uniform API, Various asynchronous operations can be handled in the same way .

We can go through Promlse Constructor to create Promise object , And encapsulate the result of an asynchronous execution inside .

Set and Map data structure

Set

The essence is similar to array , The same elements will be ignored , and java Medium Set Set similar

Map

The essence is with Object Similar structures , Difference is that ,Object A mandatory provision ket It can only be a string , and Map Structural key It can be any object

• Object yes <String,object>
• Map yes <object,object>

class

and java almost , I don't feel like writing

Generator function *

• Generatar Letter is ES6 It provides an asynchronous comprehensive solution , Grammatical behavior is totally different from traditional function
• Generator Functions have two characteristics : One is function There is an asterisk between the command and the function name ; The second is the internal use of the function body yield I define different internal states

<script>
    function * hello(){
    
        yield "hello"
        yield "niuma"
        yield "xigua"
        yield "qnm"
        return "sl"
    }
    let h = hello()
    console.log(h.next())
    console.log(h.next())
    console.log(h.next())
    console.log(h.next())
    console.log(h.next())


		// Another way 
		for(let v for h){
    
			console.log(v)
     }
</script>

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