let checkImgExists = function(url) {

      return new Promise(function(resolve, reject) {

        let ImgObj = new Image();

        ImgObj.src = url;

        ImgObj.onload = function(res) {

          resolve(res);

        }

        ImgObj.onerror = function(err) {

          reject(err)

        }

      })

    }

    checkImgExists('//www.baidu.com/img/flexible/logo/pc/result.png').then(()=>{

      //success callback

      console.log('有效链接')

    }).catch(()=>{

      //fail callback

      console.log('无效链接')

    })