javascript基础学习笔记

javascript学习笔记
// 打印
console.log(\'hello world\')
console.error(\'this is an error\')
console.warn(\'this is a warn\')

//var, let, const 声明变量

const age = 30;
age = 33
console.log(age)

String, Numbers, Boolean, null, undefined  数据类型

const name = \'john\';
const age = 30;
const x = null;
const y = undefined;
console.log(typeof x);

// 变量拼接
const name = \'John\';
const age = 30;
console.log(\'my name is \' + name + \' and i am \' + age)
console.log(`my name is ${name} and i am ${age}`)

// 字符串方法
const s =\'Hello, World\'
console.log(s.length)
console.log(s.toUpperCase())    //大写
console.log(s.toLocaleLowerCase())  //小写
console.log(s.substring(0,4))   //截取
console.log(s.split(\', \'))  //分割成数组

// 操作数组方法
const numbers = new Array(\'apples\', \'oranges\')
const numbers = [\'apples\',\'oranges\']
numbers.push(\'agee\')    //添加到数组尾部
numbers.unshift(\'one\')  //添加到数组首部
numbers.pop()   //删除最后一个数值
console.log(numbers[0])
console.log(Array.isArray(numbers)) //判断是否为数组
console.log(numbers.indexOf(\'apples\'))  //查看一个数在数组中的位置
console.log(numbers)

// 对象方法
const person = {
    fistName : \'John\',
    lastName : \'Doe\',
    age : 30,
    hobbies : [\'music\', \'moives\', \'sports\'],
    address : {
        street : \'50 main st\',
        city : \'boston\',
        state : \'MA\'
    }
}
console.log(person.fistName,person.address.city) //提取对象中的值
const {fistName, lastName, address:{city}} = person; 
console.log(fistName,city)
person.email = \'hy546880109@qq.com\'  //给对象添加键值对
console.log(person)

// for循环
for(let i=0; i<10;i++){
    console.log(`number:${i}`)
}

// while循环
let i=0;
while(i<10)
{
    i++;
    console.log(i)
} 

// for循环读取json文本
const todos = [
    {
        id: 1,
        text: \'take out trash \',
        isCompleted: true
    },
    {
        id: 2,
        text: \' out \',
        isCompleted: true
    },{
        id: 3,
        text: \'take \',
        isCompleted: true
    }
]
for(let i=0;i<todos.length;i++){
    console.log(`number:${todos[i].id}`)
    console.log(`text:${todos[i].text}`)
}
// forEach函数遍历json文本
todos.forEach(function(todo){
    console.log(todo.text)
})

// map函数遍历json文本
const todoText = todos.map(function(todo){
    return todo.text
})
console.log(todoText)

// 判断语句
const x = 4
if(x===10){
    console.log(\'x is 10\')
}else if(x>10){
    console.log(\'x > 10\')
}else{
    console.log(\'x is null\')
}

// 多重判断
const x = 10;
if(x >5 && x <8){
    console.log(\'x is true\')
}else{
    console.log(\'x is false\')
}

// 三元运算符
const x = 10
const color = x > 10 ? \'red\' : \'blue\'
console.log(color)

// switch判断
switch(color){
    case \'red\':
        console.log(\'color is red\')
        break
    case \'blue\':
        console.log(\'color is blue\')
        break
    default:
        console.log(\'color is not red or bule\')
        break
}

// 函数
function addNums(num1=1,num2=2){
    console.log(num1+num2)
}
addNums()

const address = (num1=1,num2=2)=> {
    console.log(num1+num2)
}
address()

function Person(firsName, lastName, dob){
    this.firsName = firsName
    this.lastName = lastName
    this.dob = new Date(dob)
    this.getBirthYear = function(){
        return this.bod.getFullYear()
    }
    this.getFullName = function(){
        return `${this.firsName} ${this.lastName}`
    }
}

// 类方法
class Person{
    constructor(firsName, lastName, dob){
        this.firsName = firsName
        this.lastName = lastName
        this.dob = new Date(dob)

    }
    getBirthYear(){
        return this.bod.getFullYear()
    }
    getFullName(){
        return `${this.firsName} ${this.lastName}`
    }

}
const person1 = new Person(\'John\',\'Doe\',\'4-30-1980\')
const person2 = new Person(\'Mary\',\'Smith\',\'3-6-1970\')

console.log(person1.getFullName())
console.log(person1)