JS下载文件，解决文件直接在浏览器打开的情况

JS下载文件，解决文件直接在浏览器打开的情况：

     function downloadfile(url, file_name) {
            var xmlHttp = null;
            if (window.ActiveXObject) {
                // IE6, IE5 浏览器执行代码
                xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
            } else if (window.XMLHttpRequest) {
                // IE7+, Firefox, Chrome, Opera, Safari 浏览器执行代码
                xmlHttp = new XMLHttpRequest();
            }
            //2.如果实例化成功，就调用open（）方法：
            if (xmlHttp != null) {
                xmlHttp.open("get", url, true);
                xmlHttp.send();
                xmlHttp.onreadystatechange = doResult; //设置回调函数                 
            }
            function doResult() {
                if (xmlHttp.readyState == 4) { //4表示执行完成
                    if (xmlHttp.status == 200) { //200表示执行成功
                        //引用js库：download.js
                        download(xmlHttp.responseText, file_name, "text/plain");
                    }
                }
            }
        }

download.js:

//download.js v3.0, by dandavis; 2008-2014. [CCBY2] see http://danml.com/download.html for tests/usage
// v1 landed a FF+Chrome compat way of downloading strings to local un-named files, upgraded to use a hidden frame and optional mime
// v2 added named files via a[download], msSaveBlob, IE (10+) support, and window.URL support for larger+faster saves than dataURLs
// v3 added dataURL and Blob Input, bind-toggle arity, and legacy dataURL fallback was improved with force-download mime and base64 support

// data can be a string, Blob, File, or dataURL

         
                         
                         
function download(data, strFileName, strMimeType) {
    
    var self = window, // this script is only for browsers anyway...
        u = "application/octet-stream", // this default mime also triggers iframe downloads
        m = strMimeType || u, 
        x = data,
        D = document,
        a = D.createElement("a"),
        z = function(a){return String(a);},
        
        
        B = self.Blob || self.MozBlob || self.WebKitBlob || z,
        BB = self.MSBlobBuilder || self.WebKitBlobBuilder || self.BlobBuilder,
        fn = strFileName || "download",
        blob, 
        b,
        ua,
        fr;

    //if(typeof B.bind === 'function' ){ B=B.bind(self); }
    
    if(String(this)==="true"){ //reverse arguments, allowing download.bind(true, "text/xml", "export.xml") to act as a callback
        x=[x, m];
        m=x[0];
        x=x[1]; 
    }
    
    
    
    //go ahead and download dataURLs right away
    if(String(x).match(/^data:[w+-]+/[w+-]+[,;]/)){
        return navigator.msSaveBlob ?  // IE10 can't do a[download], only Blobs:
            navigator.msSaveBlob(d2b(x), fn) : 
            saver(x) ; // everyone else can save dataURLs un-processed
    }//end if dataURL passed?
    
    try{
    
        blob = x instanceof B ? 
            x : 
            new B([x], {type: m}) ;
    }catch(y){
        if(BB){
            b = new BB();
            b.append([x]);
            blob = b.getBlob(m); // the blob
        }
        
    }
    
    
    
    function d2b(u) {
        var p= u.split(/[:;,]/),
        t= p[1],
        dec= p[2] == "base64" ? atob : decodeURIComponent,
        bin= dec(p.pop()),
        mx= bin.length,
        i= 0,
        uia= new Uint8Array(mx);

        for(i;i<mx;++i) uia[i]= bin.charCodeAt(i);

        return new B([uia], {type: t});
     }
      
    function saver(url, winMode){
        
        
        if ('download' in a) { //html5 A[download]             
            a.href = url;
            a.setAttribute("download", fn);
            a.innerHTML = "downloading...";
            D.body.appendChild(a);
            setTimeout(function() {
                a.click();
                D.body.removeChild(a);
                if(winMode===true){setTimeout(function(){ self.URL.revokeObjectURL(a.href);}, 250 );}
            }, 66);
            return true;
        }
        
        //do iframe dataURL download (old ch+FF):
        var f = D.createElement("iframe");
        D.body.appendChild(f);
        if(!winMode){ // force a mime that will download:
            url="data:"+url.replace(/^data:([w/-+]+)/, u);
        }
         
    
        f.src = url;
        setTimeout(function(){ D.body.removeChild(f); }, 333);
        
    }//end saver 
        

    if (navigator.msSaveBlob) { // IE10+ : (has Blob, but not a[download] or URL)
        return navigator.msSaveBlob(blob, fn);
    }     
    
    if(self.URL){ // simple fast and modern way using Blob and URL:
        saver(self.URL.createObjectURL(blob), true);
    }else{
        // handle non-Blob()+non-URL browsers:
        if(typeof blob === "string" || blob.constructor===z ){
            try{
                return saver( "data:" +  m   + ";base64,"  +  self.btoa(blob)  ); 
            }catch(y){
                return saver( "data:" +  m   + "," + encodeURIComponent(blob)  ); 
            }
        }
        
        // Blob but not URL:
        fr=new FileReader();
        fr.onload=function(e){
            saver(this.result); 
        };
        fr.readAsDataURL(blob);
    }    
    return true;
} /* end download() */