用<link>标签检测

function getStatus(url:string){
    return new Promise(resolve,reject){
        let link = document.createElement('link')
        link.rel="stylesheets",
        link.type="text/css"
        link.href=url;

        link.onload=function(){
            resolve(true)
        }
        link.onerror=function(){
            resolve(false)
        }
        document.body.appendChild(link)
    }
}

2.计算网络延迟

function getLoadTime(url:string){
    return new Promise(resolve,reject){
        let img= document.createElement('img')
        img.style.display=none
        img.src=`${url}/?v=${Math()*random()}`;
        const startTime = new Date()
        link.onload=function(){
            const endTime=new Date()
            resolve(endTime.getTIme()-startTime .getTime())
        }
        link.onerror=function(){
           const endTime=new Date()
            resolve(endTime.getTIme()-startTime .getTime())
        }
        document.body.appendChild(img)
    }
}