使用 Ajax 上传文件

下面的函数将选定的文件从fileEle元素发送到后端

const upload = function (fileEle, backendUrl) {
    return new Promise(function (resolve, reject) {
        // Get the list of selected files
        const files = fileEle.files;

        // Create a new FormData
        const formData = new FormData();

        // Loop over the files
        [].forEach.call(files, function (file) {
            formData.append(fileEle.name, file, file.name);
        });

        // Create new Ajax request
        const req = new XMLHttpRequest();
        req.open('POST', backendUrl, true);

        // Handle the events
        req.onload = function () {
            if (req.status >= 200 && req.status < 400) {
                resolve(req.responseText);