IPhone : Download PDF file locally in hybrid App

I am developing a hybrid app. One of the requirements is to download the PDF from a service which is returning filea as Base64 encoded string. My below code is working in browser but didn't work in android/iphone app.

downloadStatements = function(){
    // Convert the Base64 string back to text.
    var byteString = atob(encodedData);

    // Convert that text into a byte array.
    var ab = new ArrayBuffer(byteString.length);
    var ia = new Uint8Array(ab);
    for (var i = 0; i < byteString.length; i++) {
        ia[i] = byteString.charCodeAt(i);
    }

    // Blob for saving.
    var blob = new Blob([ia], { type: "application/pdf" });
    var a = document.createElement('a');
    a.href = window.URL.createObjectURL(blob);
    a.download = "test.pdf";
    a.click();
    // Tell the browser to save as report.pdf.
    //saveAs(blob, "report.pdf");
};

Hybrid or mobile app development is new for me, so I may be making some fundamental mistake. I's using angular but that itself is new to me. ;)