const checkUrl = function (url) {
  const promise = new Promise(function (resolve, reject) {
    if (!url) reject(‘无效路径‘);
    $.ajax({
      url: url,
      type: ‘GET‘,
      dataType: "jsonp", //跨域采用jsonp方式
      complete: (response)=> {
        if(response.status==200)
          resolve(true)
        else
          resolve(false)
      }
    });
  });
  return promise;
}

checkUrl(url).then(res=>{
  if(res){
      alert(‘有效‘)
  }else {
      alert(‘无效‘)
  }
});