本周学习总结

前端路由

• 那种spa应用,都是前端路由
• 后端路由成为服务器路由,对于服务器来说,会根据请求的相应的url,来找到相应的映射函数,然后执行该函数,将函数的返回值发送给客户端
• 对于前端路由来说,后端的路由映射函数通常是进行DOM的显示和隐藏操作

优缺点

后端路由优点: 安全性好,SEO好

缺点: 加大服务器压力,不利于用户体验

前端路由优点: 开发方便,只需要修改路径就可以啦,没有网络延迟,用户体验好

缺点: 浏览器的前进,退后的时候会重新发送请求,没有合理的缓存,同样不利于SEO

前端路由实现方案

• hash

  window.location.hash

• history API

  history.pushState()

  history.replaceState()

  window.history.back() 后退

  window.history.forward() 前进

  window.history.go(1) 前进1部,-2退后两次

那怎么监控history

每当同一个文档浏览历史出现变化时都会触发popState事件,只需要监控事件

window.addEventListener('popstate',function(event){
    
})

但是仅仅调用pushState 或replaceState方法,并不会触发该事件

那怎么让pushState或replaceState 事件

const _wr=function(type){
    let orig=history[type]
    return function(){
        let rv=orig.apply(this,arguments)
        let e= new Event(type)
        e.arguments=arguments
        window.dispatchEvent(e)
        return rv
    }
}
//重写方法
 history.pushState = _wr('pushState');
 history.replaceState = _wr('replaceState');
//实现监听
window.addEventListener('replaceState', function(e) {
  console.log('THEY DID IT AGAIN! replaceState 111111');
});
window.addEventListener('pushState', function(e) {
  console.log('THEY DID IT AGAIN! pushState 2222222');
});

学习angular的时候收集的一些资料

https://mlog.club/articles/3454
https://alligator.io/angular/
https://laixiazheteng.com/subject
https://blog.kevinyang.net/categories/Angular/
http://www.ngbeijing.cn/
https://rxjs-dev.firebaseapp.com/guide/observable
https://ithelp.ithome.com.tw/users/20090728/ironman/1600   Angular深入浅出三十天
https://github.com/ymfe/yapi

Array.prototype.entries()

返回一个新的Array Iterator 对象,该对象包含数组中每个索引的键/值对

let arr = ['a', 'b', 'c']
let a = arr.entries()
console.log(a.next().value)
// [0,'a']
console.log(a.next().value)
// [1,'b']
console.log(a.next().value)
// [2,'c']

串联瀑布流

const wait = value => new Promise(resolve => {
  setTimeout(() => resolve(value), 3000)
})

const fetchFoo = () => wait('foo')
const fetchBar = () => wait('bar')
const fetchBaz = () => wait('baz')
const fetchDataSlowly = async time => {
  // 串联瀑布流
  const foo = await fetchFoo()
  const bar = await fetchBar()
  const baz = await fetchBaz()
  return {foo, bar, baz, time: Date.now() - time}
}

fetchDataSlowly(Date.now())
  .then(({foo, bar, baz, time}) => {
    console.log('fetched slowly:', foo, bar, baz, time
    )
})

并联瀑布流

const wait = value => new Promise(resolve => {
  setTimeout(() => resolve(value), 3000)
})

const fetchFoo = () => wait('foo')
const fetchBar = () => wait('bar')
const fetchBaz = () => wait('baz')

const fetchDataQuickly = async time => {
  // 并行瀑布流
  const [
    foo,
    bar,
    baz
  ] = await Promise.all([
    fetchFoo(),
    fetchBar(),
    fetchBaz()
  ])
  return {foo, bar, baz, time: Date.now() - time}
}
fetchDataQuickly(Date.now())
  .then(({ foo, bar, baz, time}) => {
    console.log('fetched quickly:', foo, bar, baz, time);
  });

Object.fromEntries

类似Array,Map 把键值对转换为一个对象

let map=new Map([['a',1],['b',2],['c',3]])
console.log(Object.fromEntries(map))
// { a: 1, b: 2, c: 3 }
let arr = [['a', 1], ['b', 2], ['c', 3]]
console.log(Object.fromEntries(arr))
// { a: 1, b: 2, c: 3 }

平滑滚动到浏览器窗口的可见区域

const smoothScroll = element => 
  document.querySelector（element）.scrollIntoView（{ 
    behavior：'smooth' 
  }）; 
//平滑滚动到ID为id的元素elementID 
smoothScroll（'＃elementID'）;  

undefined和null的区别

undefined==null //true
1+null  //1
1+undefined //NaN

发现一道有意思的算法题

AAAABBCCCdFFFd
4A2B3C1d3F

const encodingStr = str => {
  if (str.length === 0) {
    return ''
  }
  let currChar = str.charAt(0)
  let count = 1
  let encoding = ''
  for (let i = 1; i < str.length; i++) {
    const char = str.charAt(i)
    if (char === currChar) {
      count++
    } else {
      encoding += count + currChar
      count = 1
      currChar = char
    }
  }
  return encoding
}
console.log(encodingStr('AAAABBCCCdFFFd'))

正则
叠词分割
let str = 'AAAABBCCCddFFFdddege'
console.log(str.match(/(.)\1*/g))
[
  'AAAA', 'BB',
  'CCC',  'dd',
  'FFF',  'ddd',
  'e',    'g',
  'e'
]

Element.animate

js动画

参数
 * 关键帧是一个对象,代表关键帧的一个集合
 * 代表动画持续时间的整数数字(毫秒单位),也可以是一个时间对象
	> duration 每次迭代的毫秒数
    >  iterations 动画重复次数
    
export class TextThreeComponent implements OnInit, AfterViewInit {
  constructor() {
  }
  public action = [{
    transform: 'rotate(0) translate3D(-50%, -50%, 0)',
    color: '#000'
  },
    {
      color: '#431236',
      offset: 0.3
    },
    {
      transform: 'rotate(360deg) translate3D(-50%, -50%, 0)',
      color: '#000'
    }
  ];
  public animation;
  timing = {
    duration: 3000,
    iterations: Infinity
  };

  ngAfterViewInit() {
  this.animation=document.querySelector('.ccc').animate(this.action, this.timing)
  }

  ngOnInit(): void {}
}

play.onclick =（）=> animation.play（）; //播放
pause.onclick =（）=> animation.pause（）; // 暂停
reverse.onclick =（）=> animation.reverse（）; // 反向