知识串讲2.0

串讲

0.1+0.2

https://blog.csdn.net/forest_fire/article/details/50944339

var x=0.1;
var y=0.2;
console.log(x+y)

数组

Var arr = new Array('猪','狗','猫');
arr.length = 0; 
console.log(arr)

let arr = new Array(100);
console.log(arr.length)

let arr = new Array('100');
console.log(arr.length)

let arr = new Array(100,101,102);
console.log(arr.length)

引用类型

var obj={
   a:'大象',
   b:['大象','李武帝','李杰']
};
var a=obj.a;
var b=obj.b;
var a= '郝金力';
b.push('苏明');
console.log(obj,a,b)

let和var区别

块级作用域和函数级作用域

var siteName="demopai"
if(true) {
   let siteName = "案例知识"
}
console.log(siteName)

var a = 100;
if(!(b in window)) {
  var b = 100;
} else {
  ++a;
}
console.log(a);
console.log(b);

call和apply

var name = 'demopai.com';
var obj = {
  name: 'baidu.com',
  getName: function () {
    var name = 'jd.com';
    return this.name;
  }
}; 
console.log(obj.getName());
console.log(obj.getName.apply()); 

var name = 'demopai.com';
var obj = {
  name: 'baidu.com',
  getName: function () {
    var name = 'jd.com';
    return this.name;
  }
}; 
console.log(obj.getName.call({number:'daxiangclass.com'})); 

构造函数执行过程

function Fn() {
 this.name='demopai'
 return []
}
var ff=new Fn();
console.log(ff);

function Fn() {
 this.name='demopai'
 return {}
}
var ff=new Fn()
console.log(ff);

function Fn() {
 this.name='demopai'
 return null
}
var ff=new Fn()
console.log(ff);

function Fn() {
 this.name='demopai'
 return undefined
}
var ff=new Fn()
console.log(ff);

function Fn() {
 this.name='demopai'
 return Symbol
}
var ff=new Fn()
console.log(ff);

function Fn() {
 this.name='demopai'
 return Boolean
}
var ff=new Fn()
console.log(ff);

function Fn() {
 this.name='demopai'
 return function(){}
}
var ff=new Fn()
console.log(ff);

数组

parseInt("2018demopai")

parseInt("demopai2018")

parseInt("20.18demopai")

可以改变this指向有哪些

call, apply, bind, eval, with, 箭头函数

数组操作,下面哪些方法会改变原数组

sort, splice, reverse

var arr = [4,2,6,7]
arr.sort();

var arr = [4,2,6,7]
arr.reverse();

var arr = [4,2,6,7]
arr.splice(2,0,100,50);

null 和 undefined

console.log(null == undefined)
console.log(null === undefined)
console.log(NaN == NaN)
console.log(NaN === NaN)
console.log(null == {})
console.log(null === {})

能提高vue项目性能的方式有

添加keep-alive
路由懒加载
抽离第三方js库
添加transition动画切换

.vue文件可独立的css作用域，通常要设置

<style  scoped></style> 
<style lang="sass"></style> 
<style lang="scss"></style> 
<style lang="stylus"></style> 

vue插值语法{{}}

data、computed中数据

vue组件通讯主要方式

父子组件
子父组件
兄弟组件
Vuex

技能作业1

用bootstrap设计表单信息收集
要求包含用户名,手机号,邮箱,地址(用三级联动),性别,兴趣爱好(多选框),个性签名
分别用bootstrap+vue+axios和bootstrap+jquery
接口:post提交到后台

技能作业2

用弹性盒实现底部导航条
收集常用图标
https://www.flaticon.com/
https://www.flaticon.com/search?word=shop

技能作业3(扩展)

用弹性布局,实现头部,内容,底部布局,底部固定