ES6语法学习(3)
函数新特新
函数参数默认值优化
<script>
//在ES6以前,我们无法给一个函数参数设置默认值,只能采用变通写法:
function add(a, b) {
// 判断b是否为空,为空就给默认值1
b = b || 1;
return a + b;
}
// 传一个参数
console.log(add(10));
//现在可以这么写:直接给参数写上默认值,没传就会自动使用默认值
function add2(a = 2, b = 1) {
return a + b;
}
console.log(add2());
</script>
多参数方式,不定参数(数组)
<script>
//2)、不定参数
function fun(...values) {
values.forEach((item, index) => {
console.log(item)
})
}
fun(1, 2) //2
fun(1, 2, 'a', 4) //4
</script>
箭头函数,lambda表达式
(java8后也有这个特性)
<script>
//3)、箭头函数。lambda
//以前声明一个方法
// var print = function (obj) {
// console.log(obj);
// }
var print = obj => console.log(obj);
print("hello");
var sum = function (a, b) {
c = a + b;
return a + c;
}
var sum2 = (a, b) => a + b;
console.log(sum2(11, 12));
var sum3 = (a, b) => {
c = a + b;
return a + c;
}
console.log(sum3(10, 20))
const person = {
name: "jack",
age: 21,
language: ['java', 'js', 'css']
}
function hello(person) {
console.log("hello," + person.name)
}
//箭头函数+解构
var hello2 = ({
name}) => console.log("hello," +name);
hello2(person);
</script>
对象优化新特性
对象的简单方法
keys方法——获取所有keys
values方法——获取所有value
entries方法——获取所有key和value
<script>
const person = {
name: "jack",
age: 21,
language: ['java', 'js', 'css']
}
console.log(Object.keys(person));//["name", "age", "language"]
console.log(Object.values(person));//["jack", 21, Array(3)]
console.log(Object.entries(person));//[Array(2), Array(2), Array(2)]
</script>
合并
key相同合并会使用最后一个
<script>
const target = {
a: 1 };
const source1 = {
b: 2 };
const source2 = {
c: 3 };
const source3 = {
b: 4 };
// 合并
//{a:1,b:2,c:3}
Object.assign(target, source1, source2, source3);
console.log(target);//["name", "age", "language"]
</script>
声明对象简写
<script>
//3)、对象的函数属性简写
let person3 = {
name: "jack",
// 以前:
eat: function (food) {
console.log(this.name + "在吃" + food);
},
//*****箭头函数this不能使用,对象.属性
eat2: food => console.log(person3.name + "在吃" + food),
eat3(food) {
console.log(this.name + "在吃" + food);
}
}
person3.eat("香蕉");
person3.eat2("苹果")
person3.eat3("橘子");
</script>
对象拓展运算符
<script>
//4)、对象拓展运算符
// 1、拷贝对象(深拷贝)
let p1 = {
name: "Amy", age: 15 }
let someone = {
...p1 }
console.log(someone) //{name: "Amy", age: 15}
// 2、合并对象
let age1 = {
age: 15 }
let name1 = {
name: "Amy" }
let p2 = {
name:"zhangsan"}
p2 = {
...age1, ...name1 }
console.log(p2)
</script>