blob文件下载

// file是要下载的文件（blob对象）

downloadHandler: function (file, fileName) {

 let link = document.createElement('a')

 link.href = window.URL.createObjectURL(file)

 link.download = fileName

 link.click()

 window.URL.revokeObjectURL(link.href)

 if (navigator.userAgent.indexOf('Firefox') > -1) {

 const a = document.createElement('a')

 a.addEventListener('click', function (e) {

  a.download = fileName

  a.href = URL.createObjectURL(file)

 })

 let e = document.createEvent('MouseEvents')

 e.initEvent('click', false, false)

 a.dispatchEvent(e)

 }

}