ES6 from getting started to mastering 04: default values and remaining parameters of functions

explain

ES6 From entry to Mastery Series （ whole 23 speak ） Learning notes .

Functions with parameter defaults

// es5  How to write it 
function add(a, b) {
    
	a = a || 666;
	b = b || 777;
	return a + b;
}
console.log(add());

function add2(a, b = 666) {
    
	return a + b;
}
console.log(add2(2));

The default expression can also be a function

function getVal(val) {
    
	return val + 1;
}
function add3(a, b = getVal(6)) {
    
	return a + b;
}
console.log(add3(3));

The remaining parameters

By three points ... And a named parameter immediately following it , such as ：...keys, This solves arguments The problem of .

// es5
function getBlogInfo(obj) {
    
	let result = Object.create(null);
	for(let i = 1; i < arguments.length; i++) {
    
		result[arguments[i]] = obj[arguments[i]];
	}
	return result;
}

let blog = {
    
	name: " Kay Xiaomo's blog ",
	author: "kaimo",
	year: "2017"
}
let blogData = getBlogInfo(blog, "name", "author", "year");
console.log(blogData);

// es6
function getBlogInfo(obj, ...keys) {
    
	console.log(keys);
	let result = Object.create(null);
	for(let i = 0; i < keys.length; i++) {
    
		result[keys[i]] = obj[keys[i]];
	}
	return result;
}

let blog = {
    
	name: " Kay Xiaomo's blog ",
	author: "kaimo",
	year: "2017"
}
let blogData = getBlogInfo(blog, "name", "author", "year");
console.log(blogData);

The remaining parameters contrast arguments：

function checkArgs(...args) {
    
	console.log(args); //  Real array 
	console.log(arguments); //  Pseudo array 
}
checkArgs("name", "author", "year");