es6（1）

1、数组的解构赋值

let [a,b,c] = [1,2,3];
console.log(a);
console.log(b);
console.log(c);
let [a,[b,c],d] = [1,[2,3],4];
console.log(a);
console.log(b);
console.log(c);
let [foo = true] = [];
console.log(foo);

2、解构的默认值，注意undefined 和 null 的区别

let [a,b="jane"] = ['jane',null];
console.log(a+b);

3、对象的结构赋值

let {foo,bar} = {foo:'jane',bar:'简'};
console.log(foo+bar);

4、圆括号
如果在解构之前就已经定义了变量，再解构就会出错

let foo;
({foo} = {foo:'jane'});
console.log(foo);

5、字符串解构

const [a,b,c,d] = 'jane';
console.log(a);
console.log(b);
console.log(c);
console.log(d);

6、扩展运算符
对象扩展运算符，编写一个方法时，允许传入的参数是不确定的，使用对象扩展运算符来作参数

function jane(...arg){
console.log(arg[0]);
console.log(arg[1]);
console.log(arg[2]);
console.log(arg[3]);
}
jane(1,2,3);

7、扩展运算符的用处

let arr1 = ['jane','chree','elaine'];
let arr2 = [...arr1];
arr2.push('janeo');
console.log(arr2);
console.log(arr1);

8、rest运算符

function jane(first,...arg){
 console.log(arg.length);
}
jane(0,1,2,3);

如何循环输出arg的值, for ... of 的循环可以避免开拓空间，增加代码运行效率

function jane(first,...arg){
 for(let val of arg){
  console.log(val);
 }
}
jane(0,1,2);

9、字符串模板

let jspang = `jane`;
let blog = `字符串模板`;
let a = 1;
let b = 2;
let result = `${a+b}`;
console.log(result);

10、查找是否存在

let jane = 'jane'; 
let blog = 'janeasdfg';
console.log(blog.includes(jane));

// 判断开头/结尾是否存在

blog.startsWith(jane);
blog.endsWith(jane);

// 复制字符串
console.log('jane'.repeat(3));