js 导出txt文件、blob流视频下载，window.open预览、打开、下载base64图片、pdf、文件

Blob流视频下载

upload(){
        // this.blob= new Blob([res.blob], {type:"video/mp4"});//从接口调用返回的
        let url = window.URL.createObjectURL(this.blob)
        console.log('url',url);
        let link = document.createElement('a')  //创建一个超链接元素
        link.style.display = 'none'
        link.href = url
        link.setAttribute('download', '下载的文件名')
        document.body.appendChild(link)
        link.click()
        document.body.removeChild(link)
      },

导出txt文件

	<button onclick="expt()">导出txtbutton>

 	function expt(){
        savefiles('文件内容','文件名称.txt')
    }
    function savefiles(data,name){
        //Blob为js的一个对象，表示一个不可变的, 原始数据的类似文件对象，这是创建文件中不可缺少的！
        var urlObject = window.URL || window.webkitURL || window;
        var export_blob = new Blob([data]);
        var save_link = document.createElementNS("http://www.w3.org/1999/xhtml", "a")
        save_link.href = urlObject.createObjectURL(export_blob);
        save_link.download = name;
        save_link.click();
    }

window.open预览、打开、下载base64图片、pdf、文件

	<button onclick="showOrDownload('data:image/jpeg;base64,4RK0RXhpZgAATU0AKgAAAAgADAEAAAMAAAA')">下载图片button>
    <button onclick="showOrDownload('data:application/pdf;base64,4AAQSkZJRgABAQAA')">打开pdfbutton>

 	function showOrDownload(base64String) {
        //这里截取后的fileHeader是data:image/jpeg
        var fileHeader = base64String.slice(0, base64String.indexOf(";base64"));
        //图片格式的imageType是image，所以就不用判断具体的图片类型了
        var imageType = fileHeader.slice(fileHeader.indexOf(":") + 1, fileHeader.indexOf("/"));
        if (imageType === 'image') {
            //图片下载
            this.base64StringToDownload(base64String);
            // 图片预览
            // this.showImage(base64String);
            return;
        }
        var fileType = fileHeader.slice(fileHeader.indexOf("/") + 1);
        if (fileType === 'pdf') {
            //pdf预览
            this.showPdf(base64String);
            return;
        }
        //其他类型文件只能下载
        this.base64StringToDownload(base64String);
    }
    function showImage(base64String) {
        const img = new Image();
        img.src = base64String;
        const newWin = window.open("", "_blank");
        newWin.document.write(img.outerHTML);
        newWin.document.title = "附件";
        newWin.document.close();
    }
    function showPdf(base64String) {
        var pdfResult = base64String;
        let pdfWindow = window.open("");
        pdfWindow.document.write("");
        pdfWindow.document.title = "附件"
        pdfWindow.document.close();
    }
    function base64StringToBlob(base64String) {
        var arr = base64String.split(','),
            mime = arr[0].match(/:(.*?);/)[1],
            bstr = atob(arr[1]),
            n = bstr.length,
            u8arr = new Uint8Array(n);
        while (n--) {
            u8arr[n] = bstr.charCodeAt(n);
        }
        return new Blob([u8arr], {type: mime});
    }
    function base64StringToDownload(base64String) {
        //生成唯一的文件名，长度可以自己定义
        const id = Number(Math.random().toString().substr(3, 5) + Date.now()).toString(36);
        let blob = this.base64StringToBlob(base64String);
        let url = URL.createObjectURL(blob)
        let save_link = document.createElementNS("http://www.w3.org/1999/xhtml", "a")
        save_link.href = url
        save_link.download = "附件" + id;
        save_link.click();
    }