Download blob client side

downloader.js

const download = blob => {
    if (window.navigator.msSaveOrOpenBlob) {  // IE hack; see http://msdn.microsoft.com/en-us/library/ie/hh779016.aspx
        window.navigator.msSaveBlob(blob, "filename.csv");
    } else {
        let a = window.document.createElement("a");
        a.href = window.URL.createObjectURL(blob, {type: "text/plain"});
        a.download = "filename.csv";
        document.body.appendChild(a);
        a.click();  // IE: "Access is denied"; see: https://connect.microsoft.com/IE/feedback/details/797361/ie-10-treats-blob-url-as-cross-origin-and-denies-access
        document.body.removeChild(a);
    }
}

// usage
const blob = new Blob([csvString]);
download(blob)