ES6 -- formal parameter setting initial value, extension operator, iterator, and generating function

Formal parameter setting initial value

characteristic

（1） Be similar to python Set the initial value of the formal parameter of

（2） Parameters with default values , All in the back

            function add(a, b, c = 10) {
                return a + b + c;
            }

            console.log(add(1, 2))  // 13
            let options = [1, 2, 3, 4, 5]
            console.log(add(...options)) // 6

Extension operator

characteristic ：

（1） Convert the array to a comma separated sequence of parameters

            const TF_BOYS = [' Jackson Yi ', ' hanah ', ' Juen-Kai Wang ']
            function chunwan() {
                console.log(arguments) // ' Jackson Yi ', ' hanah ', ' Juen-Kai Wang '
            }

            chunwan(...TF_BOYS)

            //  Array merge 
            const KUAI_ZI = [' Wang Taili ', ' Xiao Yang ']
            const FENG_HUANG = [' Zeng Yi ', ' Linghua ']
            console.log(KUAI_ZI.concat(FENG_HUANG))
            console.log([...KUAI_ZI, ...FENG_HUANG]) //  The performance is much higher than concat

			//  Copy of , If there is a reference type , It's a light copy 
			let kuai_zi1 = [...KUAI_ZI]

（2） Object extension operator

Object extension operations can be used for object merging , Regenerate the rest directly into an object, etc , Expanding is similar to a Map

            const CONFIG = {
                host: '127.0.0.1',
                port: '3306',
                username: 'root',
                password: 'root'
            }

            function connect({host, port, ...user}) {
                console.log(host)
                console.log(port)
                console.log(user)
            }

            connect(CONFIG)

            const CONFIG1 = {
                type: 'oracle'
            }
            const CONFIG2 = {
                cmd: 'sqlplus'
            }

            console.log({...CONFIG, ...CONFIG1, ...CONFIG2})

iterator

characteristic

（1）Array、Arguments、Set、Map、String、TypeArray、NodeList Deployed Iterator Interface （ An attribute in an object ） Can use iterators to traverse

（2） You can customize [Symbol.iterator] Method , Define the elements in the traversal object , I feel a little silly

Silicon Valley Web front end ES6 course , cover ES6-ES11_ Bili, Bili _bilibili

            const XIYOU = [' Tang's monk ', ' The Monkey King ', ' Pig eight quit ', ' Monk sha ']
            for (let item of XIYOU) {
                console.log(item)
            }

            for (let item of ' I am the king of ox horn '){
                console.log(item)
            }

Generator function

characteristic ：

（1） Asynchronous programming , Pure callback functions

			function * generator() {
			    console.log(111)
				yield ' Never had ears '  // yield Code segmentation , It can be used for segmented debugging ,next Just pass in the arguments , Asynchronous programming parameter passing 
                console.log(222)
				yield ' Never had a tail '
                console.log(333)
				yield ' It's strange. '
                console.log(444)
            }

            let iterator  = generator();
			// iterator.next() // 111
			// iterator.next() // 222
			// iterator.next() // 333
			// iterator.next() // 444
			for (let item of iterator){
			    console.log(item)
			}

Asynchronous programming

JavaScript It's single threaded , Using asynchronous mode can avoid thread switching , Save resources , But the native writing is difficult to read and view

            //  Traditional callback functions 
            setTimeout(() => {
                console.log(' Callback programming ')
	            setTimeout(()=>{
	                console.log(' Wait first 2s Besides, ')
	            },2000)
            }, 2000)
			console.log(' You will see me immediately ')

 Promise Solution --  Study alone