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)
 
 
 

__EOF__

本文作者：Harry
本文链接：https://www.cnblogs.com/harry66/p/14136309.html
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