JavaScript使用a标签下载文件

function(file_type){
   let url = '文件的url地址'  
   let file_suffix = { // 后缀
    img: '.jpg',
    video: '.mp4',
   }
   let file_name = 'file' +  file_suffix[file_type] // 文件名
   let create_a_dom = document.createElement('a')
   document.body.append(create_a_dom)
   create_a_dom.href = url
   create_a_dom.download = file_name
   create_a_dom.rel = 'noopener noreferrer'
   create_a_dom.click()
   document.body.removeChild(create_a_dom)  
}

 svg字符串（res就是svg的字符串）转为URL后下载：

let blob = new Blob([res], {
      type: 'image/svg+xml',
     })
     let url = URL.createObjectURL(blob)
     let create_a_dom = document.createElement('a')
     document.body.append(create_a_dom)
     create_a_dom.href = url
     create_a_dom.download = this.download_file.name
     create_a_dom.rel = 'noopener noreferrer'
     create_a_dom.click()
     document.body.removeChild(create_a_dom)