手写AJAX

完整版

var xhr = new XMLHttpRequest()
xhr.open('GET','xxx')
xhr.onreadystatechange = function(){
    if(xhr.readyStatus ===4 ){
        if(xhr.status >= 200 && xhr.status <300 || xhr.status ==304){
            console.log('success')
        }else{
            console.log('error')
        }
    }
}

xhr.send()

简洁版

var xhr = new XMLHttpRequest()
xhr.open('GET', 'xxx')
xhr.onload() =function(){
    if(xhr.status >=200 && xhr.status<300 || xhr.status === 304){
        console.log('请求成功')
    }else{
        console.log('请求失败')
    }
}
xhr.send()

手写事件代理

$('ul').addEventListener('click', function(e){
  if(e.target.tagName.toLowerCase() === "li"){
    console.log('点击了li')
  })
})
``` `