download-upload-files.js

(function () { // initiates a file download in the browser for files generated in the C# code window.saveFile = function (bytesBase64, mimeType, fileName) { var fileUrl = "data:" + mimeType + ";base64," + bytesBase64; fetch(fileUrl) .then(response => response.blob()) .then(blob => { var link = window.document.createElement("a"); link.href = window.URL.createObjectURL(blob, { type: mimeType }); link.download = fileName; document.body.appendChild(link); link.click(); document.body.removeChild(link); }); }

// provides file content for files selected in JS to C# without saving on the server
window.getUploadedFile = (inputID) => {
    var inputEl = document.getElementById(inputID);
    if (inputEl.files.length == 0) {
        return "";
    }
    else if (inputEl.files[0].size > (4 * 1024 * 1024)) { // 4MB
        inputEl.value = "";
        alert("File size too large. Max allowed size is 4MB.");
        return "";
    }
    else if (inputEl.accept.length && inputEl.accept.indexOf(inputEl.files[0].name.split('.').pop()) < 0) {
        inputEl.value = "";
        alert("Allowed file types: " + inputEl.accept);
        return "";
    }
    const fileReader = new FileReader();
    return new Promise((resolve) => {
        fileReader.onloadend = function (e) {
            var data = {
                fileName: inputEl.files[0].name,
                fileData: e.target.result.split('base64,')[1]
            };
            resolve(data);
        };
        fileReader.readAsDataURL(inputEl.files[0]);
    });
};

})();