前端技术发展史、Nodejs语法

HTML

浏览器

历史

浏览器技术

JavaScript

JS

 ES

V8引擎

CSS(Cascading Style Sheets)层叠样式表

动态网页技术

网页布局

同步

异步

前端开发

硬件发展

 

ES6开发环境准备及基础语法(Nodejs)

 Nodejs

 

安装

国内镜像可以去阿里云镜像
https://npm.taobao.org/mirrors/node

开发

文档

搜索MDN，Mozilla Developer Network，提供非常完善HTML、CSS、JS等技术资料。 
https://developer.mozilla.org/zh-CN/docs/Web/JavaScript

指南(非常好的JS文档)
https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Guide

使用任何一种文本编辑器，都可以开发JS，此次使用微软的Visual Studio Code开发。

Visual Studio Code

下载 https://code.visualstudio.com/Download

解决快捷键冲突

注释

 

str = 'hello' + /*comment*/ 'magedu'
console.log(str)
//结果如下
//hellomagedu

常量和变量

str = 'hello' + /*comment*/ 'magedu'
console.log(str)

var a
let b
console.log(1,a,b)

a = 1
b = 'a string'
console.log(2,a,b)

// const c;  不可以
const c = 100
console.log(c)

//c = 200 不可以修改

var y // 只是声明，y值为undefined
var x = 5 //规范的声明并初始化，声明全局或全局变量
x = 6 /*不规范的初始化，不推荐。在严格模式下会产生异常。在赋值之前不能引用，因为它没有声明。一旦这样赋值就是全局作用域*/

function hello()
{
    var a   //只是声明，a为undefined，作用域在函数中
    a = 100
}

console.log(a) //未声明变量异常，ReferenceError: a is not defined

// a = 200 // 不能提升作用域
// var a = 200 ;hello(); // var提升作用域

数据类型

 

// 类型转换
// 弱类型
console.log('======string======')
console.log(a = 3 + 'magedu',typeof(a)) //3magedu string
console.log(a = null + 'magedu',typeof(a))//nullmagedu string
console.log(a = undefined + 'magedu',typeof(a))//undefinedmagedu string
console.log(a = true + 'magedu',typeof(a))//truemagedu string

//  数字
console.log('========number=====')
console.log(a = null + 8, typeof a)//8 number
console.log(a = undefined + 8, typeof a)//NaN number
console.log(a = true + 8, typeof a)//9 number
console.log(a = false + 8, typeof a)//8 number

// boolean
console.log('========bool====')
console.log(a = null + true,typeof a)//1 number
console.log(a = null + false,typeof a)//0 number
console.log(a = undefined + true,typeof a)//NaN number
console.log(a = undefined + false,typeof a)//NaN number
console.log(a = null & true,typeof a)//0 number
console.log(a = undefined & true,typeof a)//0 number

//短路
console.log('=======短路========')
console.log(a = null && true,typeof a)//null object
console.log(a = false && null,typeof a)//false boolean
console.log(a = false && 'magedu',typeof a)//false boolean
console.log(a = true && 'magedu',typeof a)//magedu string
console.log(a = true && '',typeof a)// string

//
console.log('=======null======')
console.log(a = null + undefined,typeof a)//NaN number

字符串

let a = 'abc';
let b = "124";
let c = `line1
    line2
line3
`//支出多行
console.log(c)

//字符串插值，要求在反引号字符串中。Python3.6支持
let name = "tom",age =19
console.log(`Hi my name is ${name},I am ${age}`)

转义字符

字符串操作方法

let school = 'magedu'
console.log(school.charAt(2))//g
console.log(school[2])//g
console.log(school.toUpperCase())//MAGEDU
console.log(school.concat('.com'))//连接
console.log(school.slice(3))//切片，支持负索引
console.log(school.slice(3,5))
console.log(school.slice(-2,-1))
console.log(school.slice(-2))

let url = 'www.magedu.com'
console.log(url.split('.'))
console.log(url.substr(7,2))//返回子串从何处开始，取多长
console.log(url.substring(7,10))//返回子串，从何处开始，到什么为止

let s = 'magedu.com'
console.log(s.indexOf('ed'))//3
console.log(s.indexOf('ed',4))//7
console.log(s.replace('.edu','.com'))
s = '	mag edu 
'
console.log(s.trim())//去除两端的空白字符。

数值型number

 

console.log(Number.MAX_VALUE)//1.7976931348623157e+308
console.log(Number.MIN_VALUE)//5e-324
console.log(Number.POSITIVE_INFINITY)//Infinity
console.log(Number.NEGATIVE_INFINITY)//-Infinity
console.log(Number.NaN)//NaN

数字的方法

 

console.log(Math.PI)
console.log(Math.abs(-1))
console.log(Math.log2(16))
console.log(Math.sqrt(2))
console.log(Math.random())

运算符

算数运算符

let i = 0;
let a = i++;
console.log(a,i)// 0 1
console.log(a,i++)//0 1
a = ++i
console.log(a,i)//3,3

挑战题

比较运算符

 

console.log(100>'200')//false
console.log(300>'200')//true
console.log(300>'2000')//false
console.log(3000>'2a')//false
console.log('3000'>'2000')//true
//宽松比较
console.log(300 == '300')//true
console.log('200' == '200')//true
//严格比较 ===
console.log(300 === '300')//false
console.log('300' === '300')//true

 

逻辑运算符

位运算

 

三元运算符

 

console.log(('3'>30)?'true':'false')//false

逗号运算符

let a = 4+5,b = true, c = a >20?'true':'false'
console.log(a)//9
console.log(c)//false

其他

console.log('a' instanceof String)//false
console.log(1 instanceof Number)//false
a = new String('b')
console.log(a instanceof String)//true
console.log(a instanceof Object)//true
console.log(new Number(1) instanceof Number)//true

console.log(typeof('a'))//string
console.log(typeof 'a')//string
console.log(typeof a)//object
console.log(typeof typeof a)//string

x = 42;
var y = 43; 
let z = 60;
myobj = new Number();
myobj.h = 4
console.log(delete x );//true   (can delete if delcared implicitly)
console.log(delete y );//false  (cannot delete if declared with var)
console.log(delete z );//false  (cannot delete if declared with let)
console.log(delete Math.PI );   //false    (cannot delete predefined properties)
console.log(delete myobj.h );   //true     (can delete user-defined properties)
console.log(delete myobj );     //true     (can delete if delcared implicitly)

var trees = new Array("redwood","bay","cedar","oak","maple")
for (var i=0;i<trees.length;i++)
    console.log(trees[i])
console.log("==================") 
delete trees[3]//数组中元素被删除，但空着的位置是undefined
for (var i=0;i<trees.length;i++)
    console.log(trees[i])

var trees = new Array("redwood","bay","cedar","oak","maple")
console.log(0 in trees)         // true，0在数组对象的index中  
console.log(6 in trees)         // false，6不在数组对象的index中
console.log("bay" in trees)     // false，bay不是属性，它是值
console.log("length" in trees)  // true，length是对象的属性

delete trees[3]
console.log(3 in trees) //false

//Custom objects
let mycar ={
    color:"red",
    year:1998
}
console.log("color" in mycar)   //true
console.log("model" in mycar)   //false
console.log("year" in mycar)    //true

运算符优先级

 

表达式

 

function* inc()
{
    let i = 0;
    let j = 3;
    while (true){
        yield i++;
        if (!j--) return 100;
    }
}
let gen = inc()
for (let i=0;i<6;i++)
    console.log(gen.next());
/*输出结果如下：
{ value: 0, done: false }
{ value: 1, done: false }
{ value: 2, done: false }
{ value: 3, done: false }
{ value: 100, done: true }
{ value: undefined, done: true }
 */ 

JS语法

语句块

//语句块
function hello(){
    let a = 1;
    var b =2;
    c =3;
}
// let d = 100
if (1){
    let d = 4;
    var e = 5;
    f = 6;
    if (true){
        console.log(d)//4
        console.log(e)//5
        console.log(f)//6
        console.log('===============')
        g = 10
        var h = 11
    } 
}

console.log(a)//不可见
console.log(b)//不可见
console.log(c)//函数内不可见
console.log(d)//块作用域使用let，快外不可见；
console.log(e)//块作用域使用var，可见    //5
console.log(f)//块作用域隐式声明，可见   //6
console.log(g)//可见         //10
console.log(h)//可见         //11

流程控制

条件分支

条件的False等效：
    False
    undefined
    null
    0
    NaN
    空字符串
其他值都被视为True

switch...case分支语句

 

let x =5;
switch (x){
    case 0:
        console.log('zero')
        break;
    case 1:
        console.log('one')
    case 2:
        console.log('two')
    case 3:
        console.log('three')
        break;
    case 5:
    case 4:
        console.log(4)
    default:
        console.log('other')
}

for循环

for (let i=0;i<10;i++){
    console.log(i)
}
for (var x=0,y=9;x<10;x++,y--)
    console.log(x*y)

while循环和do...while循环

 

let x =3;
while (x--){
    console.log(x)
}
console.log('~~~~~~')
do{
    console.log(x);
}while(x++<3)
console.log(x)
/*输出结果
2
1
0
~~~~~~
-1
0
1
2
3
4
*/

练习

 

for(let i=1;i<10;i++){
    line = '';
    for (let j=1;j<=i;j++)
        line += `${j}*${i}=${i*j} `;
    console.log(line)
}

for...in循环

let arr = [10,20,30,40]
console.log(arr[1])
for (let x in arr)
    console.log(x)//返回索引

for (let index in arr){
    console.log(`${index}:${arr[index]}`)//插值
}
//C风格
for(let i=0;i<arr.length;i++){
    console.log(arr[i])
}
//对象
let obj = {
    a:1,
    b:'magedu',
    c:true
}
console.log(obj.a)
console.log(obj['b'])
console.log(obj.d)//undefined

for (let x in obj){
    console.log(x)//属性名
}

for (let key in obj){//返回数组的index
    console.log(`${key}:${obj[key]}`)//插值
}

for...of循环

 

let arr =  [1,2,3,4,5]
let obj = {
    a:1,
    b:'magedu',
    c:true
}

for (let i of arr){//返回数组的元素
    console.log(i)
}

for (let i of obj){//异常，不可以迭代
    console.log(i)
}

break、continue

for迭代的差别

//for迭代的差别
function sum(arr){
    for (let x in arr){//遍历index
        console.log(x,typeof x,arr[x])
    }
    for (let x of arr){//遍历元素
        console.log(x,typeof x)
    }
    for (let x=0;x<arr;x++){//自定义索引数值遍历
        console.log(x,typeof x,arr[x])
    }
}
sum([3,6,9])

函数

 

函数表达式

//匿名函数
const add = function(x,y){
    return x + y;
};
console.log(add(4,6));

//有名字的函数表达式
const sub = function fn(x,y){
    return x - y;
};
console.log(sub(5,3))
// console.log(fn(5,3))//fn只能用在函数体内部

const sum = function _sum(n){
    if (n==1) return n;
    return n + _sum(--n)//_sum只能内部使用
}
console.log(sum((4)))

函数、匿名函数、函数表达式的差异

console.log(add(4,6))
function add(x,y){//声明提升
    return x + y;
};

//console.log(sub(5,3));//sub未定义
//有名字的函数表达式
const sub = function(x,y){
    return x - y;
}
console.log(sub(5,3))

高阶函数

const counter = function(){
    let c = 0;
    return function(){
        return ++c;
    };
};

const c = counter()
console.log(c())//1
console.log(c())//2
console.log(c())//3

const map = function(arr,fn){
    let newarr = [];
    for (let i in arr){
        newarr[i] = fn(arr[i])
    }
    return newarr
}
console.log(map([1,2,3,4],function(x){return ++x}))

var map = function* (fn,arr){
    for (i in arr)
        yield fn(arr[i]);
};
let newarr = map(x => x+10,[1,2,3])
for (x of newarr){
    console.log(x)
}

箭头函数

//以下三行等价
console.log(map([1,2,3],(x) => {return x*2}))
console.log(map([1,2,3],x => {return x*2}))
console.log(map([1,2,3],x => x*2))

函数参数

普通参数

 

const add = (x,y) => x+y;
console.log(add(4,5));//9

const add1 = (x,y=5) => x+y;
console.log(add1(4,6));//10
console.log(add1(4));//9

const add2 = (x=6,y) => x+y;
console.log(add2());//NaN
console.log(add2(1));//NaN
console.log(add2(y=2,z=3));//5

可变参数(rest parameters剩余参数)

 

//可变参数
const sum = function(...args){
    let result = 0;
    for (let x in args){
        result += args[x];
    }
    return result
}
console.log(sum(3,6,8))//17
console.log(sum((3,6,8)))//8
console.log(sum([3,6,8]))//03,6,8

arguments对象

(function (p1,...args){
    console.log(p1)
    console.log(args)
    console.log('---------------')
    console.log(arguments,typeof arguments)
    for (let x of arguments)//{ '0': 'abc', '1': 1, '2': 3, '3': 5 } 这里没报异常！？
        console.log(x)
    for (let x in arguments)
        console.log(x)
})('abc',1,3,5)

let arguments = {'0': 'abc', '1': 1, '2': 3, '3': 5}
console.log(arguments,typeof arguments)
for (let x in arguments)
    console.log(x)
for (let x of arguments)//报异常
    console.log(x)

((x,...args) => {
    console.log(args);//数组
    console.log(x);
    console.log(arguments);//不是传入的值
})(...[1,2,3,4])

参数解构

 

const add = (x,y) => {console.log(x,y);return x,y}
console.log(add(...[100,200]))//   100 200  200
console.log(add(...[100,200,300,3,5,5]))// 100 200 200
console.log(add(...[100]))//100 undefined undefined

函数返回值

 

const add = (x,y) => {return x,y}
console.log(add(4,100))//110

a = (x=5,y=6,true)
console.log(a)//true
b = (123,true,z='test')
console.log(b)//test
function c(){
    return x=5,y=6,true,'ok'
}
console.log(c())//ok

作用域

//test1.js
//函数中变量的作用域
function tets(){
    a = 100;
    var b = 200;
    let c = 300;
}
//先要运行test函数
tets()
console.log(a)
// console.log(b)//不可见
// console.log(c)//不可见

//test2.js
//块作用域中变量
if(1){
    a = 100;
    var b = 200;
    let c = 300;
}
console.log(a)
console.log(b)
// console.log(c)//不可见