Javascript Android webview Bolb检查mime类型

这是集成了android webview的javascript代码

if(blobUrl.startsWith("blob")){
        return "javascript: var xhr = new XMLHttpRequest();" +
            "xhr.open('GET', '"+ blobUrl +"', true);" +
            "xhr.setRequestHeader('Content-type','application/pdf');" +
            "xhr.responseType = 'blob';" +
            "xhr.onload = function(e) {" +
            "    if (this.status == 200) {" +
            "        var blobPdf = this.response;" +
            "        var reader = new FileReader();" +
            "        reader.readAsDataURL(blobPdf);" +
            "        reader.onloadend = function() {" +
            "            base64data = reader.result;" +
            "            Android.getBase64FromBlobData(base64data);" +
            "        }" +
            "    }" +
            "};" +
            "xhr.send();";
    }
    return "javascript: console.log('It is not a Blob URL');";

如何检查url mime类型？ 类似的

if(Urlblob ==image/png)

运行此javascript代码