3、数据类型
3.1、字符串
3.2、数组
3.3、对象
var person = {
firstName: "Bill",
lastName : "Gates",
id : 678,
fullName : function() {
return this.firstName + " " + this.lastName;
}
};
console.log(person.firstname);
console.log(person.fullName());
3.4、流程控制
let age = 3;
if (age > 3) {
alert("大于3岁了");
} else {
alert("不到3岁");
}
循环:
while (age < 100) {
age++;
console.log(age);
}
for (let i = 0; i < 100; i++) {
console.log(i);
}
数组循环
var arr = [1, 4, 3];
for (let i = 0; i < arr.length; i++) {
console.log(arr[i]);
}
for (let num of arr) {
console.log(num)
}
forEach 循环
let arr = [2, 3, 4];
arr.forEach(function (value) {
console.log(value);
});
3.5、Map 和 Set
ES6 新特性
Map:
let map = new Map([['tom', 100], ['jack', 90]]);
let number = map.get('tom');
console.log(number);
map.set("admin", 10000);
map.delete('admin');
Set:
let set = new Set([1, 2, 3, 4, 1, 1]);
set.add(5);
set.delete(5);
let has = set.has(4);
console.log(has);
3.6、iterator迭代器
ES6 新特性
var arr = [1, 4, 3];
for (let i = 0; i < arr.length; i++) {
console.log(arr[i]);
}
for (let num of arr) {
console.log(num)
}
遍历Map
for (let mapElement of map) {
console.log(mapElement);
}
遍历Set
for (let number1 of set) {
console.log(number1);
}
4、函数
4.1、函数定义及调用
方式一
function abs(x) {
if (x >= 0) {
return x;
} else {
return -x;
}
}
let x = abs(10);
方式二
let abs = function (x) {
if (x >= 0) {
return x;
} else {
return -x;
}
}
let x = abs(-99);
不传参
let abs = function (x) {
if (typeof x !== 'number') {
throw 'not a number';
}
if (x >= 0) {
return x;
} else {
return -x;
}
}
arguments: 获取所有参数
let abs = function (x) {
for (let i = 0; i < arguments.length; i++) {
console.log(arguments[i]);
}
if (x >= 0) {
return x;
} else {
return -x;
}
}
let x = abs(-99, -11, 1, 2, 3);
rest参数,获取除声明之外的参数
console.log("a=>" + a);
console.log("b=>" + b);
for (let restElement of rest) {
console.log(restElement);
}
4.2、变量的作用域
- 局部变量
- 全局变量
- 常量 const
4.3、方法
- 定义在对象内部
- 定义在外部
- 调用的时候要加括号(如果在对象内部调用,只写名字)
5、内部对象
标准对象
typeof 123
"number"
typeof "123"
"string"
typeof true
"boolean"
typeof NaN
"number"
typeof []
"object"
typeof {}
"object"
typeof Math.abs
"function"
typeof undefined
"undefined"
5.1、Date
let now = new Date();
now.getFullYear()
now.getMonth()
now.getDate() // 日
now.getDay() // 周几
now.getHours()
now.getMinutes();
now.getSeconds();
now.getTime(); // 时间戳
5.2、JSON
- 对象都用{}
- 数组都用[]
- 所有的键值对都用 key : value
let user = {
"name": "faddei",
"age": 24,
"sex": "male"
};
let str = JSON.stringify(user); // 将对象转换成字符串,'{"name":"faddei","age":24,"sex":"male"}'
let obj = JSON.parse('"{"name":"faddei","age":24,"sex":"male"}"'); // 将字符串转换成对象