AJAX上传文件

 function up_files() {
        var fileSelect = document.getElementById('file-select');
        var files = fileSelect.files;

        var formData = new FormData();

        for (var i = 0; i < files.length; i++) {
            var file = files[i];

            if (!file.type.match('image.*')) {
                continue;
            }

            formData.append('photos[]', file, file.name);
        }

        var xhr = new XMLHttpRequest();

        xhr.open('POST', 'test.php', true);

        xhr.onload = function () {
            if (xhr.status !== 200) {
                alert('An error occurred!');
            }
        };

        var progressBar = document.getElementById('progress');
        xhr.upload.onprogress = function(e) {
            if (e.lengthComputable) {
                progressBar.value = (e.loaded / e.total) * 100;
                progressBar.textContent = progressBar.value; // Fallback for unsupported browsers.
            }
        };

        xhr.send(formData);
    }

<div id="progress" style="width: 100px;height: 100px;background-color: #0baae4">Test content</div>
<input type="file" id="file-select" name="photos[]" multiple/>
<button onclick="up_files()">上传</button>

test.php 中使用$_FILES 来获取文件信息

原文链接:http://javascript.ruanyifeng.com/bom/ajax.html#toc21