First, new data types Symbol
concept:
Symbol representative of the unique
Value generated by Symbol Symbol type function, while the function returns a value Symbol only
Symbol strings function may receive as parameters, but the same even if the value returned is the only parameter
effect:
Property privatization
Data protection
没有参数的情况
var s1 = Symbol();
var s2 = Symbol();
s1 === s2 // false
有参数的情况
var s1 = Symbol("foo");
var s2 = Symbol("foo");
s1 === s2 // false
var mySymbol = Symbol();
// 第一种写法var a = {};
a[mySymbol] = 'Hello!';
// 第二种写法var a = {
[mySymbol]: 'Hello!'
};
// 第三种写法var a = {};
Object.defineProperty(a, mySymbol, { value: 'Hello!' });
Object.getOwnPropertySymbols(obj) 枚举symbol的key值
注意:Symbol作为对象的key值得时候不能被for in进行遍历
Second, block-level scope
concept:
In all the ES6 code is wrapped {} block-level scope, all variables used in the block-level scope let const declared in a temporary dead
{
let a = 20;
}
console.log(a);//报错
Three, var let const variable declaration
Compare different
var
支持变量声明与解析
不支持块级作用域
允许重复声明
let
不支持变量声明与解析
支持块级作用域
不允许重复声明
用let声明的变量或者方法只会在代码块中有效
{
let a = 10;
var b = 20;
}
console.log(a);//报错
const
不支持变量声明与解析
支持块级作用域
不允许重复声明
声明常量,一旦确定不允许被修改
声明常量必须赋值 不能跟var 一样声明后再定义
Fourth, deconstruction assignment
concept:
Allow according to a certain pattern, the value extracted from the object and the array
// 数组解构
let [a,b,c] = [1,2,3];
// 对象解构
let {name,age} = {name:"张三",age:19};
// 注意对象解构 key值必须一一对应
// 对象解构+别名
let {name : _name , top : _top } = {name:"张三",top:20}
// 因为name和top属于关键字,因此我们可以通过别名的方式来更改名称
// 多重解构
let {obj : { name }, arr:[ a, b]} = {obj:{name:"张三"},arr:[10,20]}
// 案例:
let {letf:l , top: t} = document.getElementById("box");
Fifth, with the expansion operator
concept:
Or converting the array of objects into comma separated sequence parameter sequence
effect:
1, the combined arrays, objects
2, the remaining function parameters
3, alternative arguments
// 数组合并
var arr = [10,20,30];
var arr1 = [40,50,60];
var newArr = [...arr,...arr1];
// 展开数组
console.log(Math.max(...arr));
// 对象合并
var obj = {width:100,height:200};
var obj2 = {left:100,top:200};
var newObj = {...obj,...obj2};
Six String template
1, need to wrap the string is too long how to do?
// 常规解决方案:
var a = '<div>'+
'<span>'+num+'</span>'+
'div>';
// ES6神器:
var b = `
<div>
<span></span>
</div>
`;
2, string concatenation too much trouble how to do?
// ES6神器(字符串模板):
var phone = 18200000000;
var intro = `my name is pine, my phone is ${phone}`;
console.log(intro); //${phone}被替换成18200000000
/*
说明:
1、使用 `` 反单因号 代替 '' 或者 ""
2、使用 ${变量} 实现变量拼接
*/
3, includes string search
// 之前使用indexOf进行查找,利用的是indexOf方法的特性,找打了返回下标,
// 找不到返回-1,所以每次你需要这么写:
var str = 'abcd';
if( str.indexOf('c') > -1 ){} //需要判断是否>-1
// ES6神器:includes方法
// str.includes(查找的内容); 找到返回true,找不到返回false
var str = 'good method!';
str.includes('method'); //true
4, it is determined inclusive startsWith endsWith
/*
startsWith用于判断是否位于头部,
endsWith判断是否位于尾部,
可以说这两个方法是includes方法的扩展
*/
let str = 'how are you?';
str.startsWith('how');//true
str.endsWith('?');//true
5, repeat repeat string (lazy Welfare)
//str.repeat(n); 将字符串重复n次(n是整数)
let str = 'money';
str.repeat(2); // 'moneymoney'
Seven new object methods
1, abbreviated object
var a = 10;
var obj = {a}
//等价
var obj = {a:10};
//当key值与value值一样的时候我们可以写一个
2、Object.is
//判断2个对象是否指向同一个内存地址
var obj = {a:1,b:2};
var obj1 = obj
Object.is(obj,obj1);// true
3、Object.assign
//Object.assign 合并对象
var obj = {name:"Alley",age:18};
var obj2 = {sex:"男"}
var newObj = Object.assign(obj,obj2);
console.log(newObj); //{name:"Alley",age:18,sex:"男"}