手写一个promise
class Promise{
succeed = null
failed = null
state = 'pending'
constructor(fn){
fn(this.resolve.bind(this),this.reject.bind(this))
}
resolve(result){
this.state = 'fulfilled'
this.succeed(result)
}
reject(reason){
this.state ='rejected'
this.failed(reason)
}
then(succeed,failed){
this.succeed = succeed
this.failed = failed
}
}
const getWeather = city => new Promise((resolve,reject) =>{
let xhr = new XMLHttpRequest
let url = 'http://rap2api.taobao.org/app/mock/244238/getWeather?city='+city
xhr.open('GET',url,true)
xhr.onload = () => {
if(xhr.status === 200){
return resolve(JSON.parse(xhr.responseText))
}else{
return reject(`获取${city}天气失败`)
}
}
xhr.send()
})
getWeather('上海').then(function (value){console.log(value)}
,function(error){console.log(error)})
