我正在使用表单字段上载多个文件
<input type="file" accept="image/jpeg, image/png" multiple
循环将所有文件发送到上传功能
// Upload photo function
var upload = function (photo, callback) {
var formData = new FormData();
formData.append('photo', photo);
var request = new XMLHttpRequest();
request.onreadystatechange = function() {
if (request.readyState === 4) {
callback(request.response);
}
}
request.open('POST', 'upload.php');
request.responseType = 'json';
request.send(formData);
};
for (var i = 0; i < files.length; i++) {
upload(resizedFile, function (response) { });
}
如果所有文件均已成功上传,请重定向..
//all files finished, go to ...
if(response !== null && typeof response !== 'object') var response = JSON.parse(response);
window.location.href = "my-new-url.php?id="+response.id;
我的问题,重定向是在所有上传完成之前完成的。如何使脚本等待所有xmlhttprequest完成?
我更改了这样的上传功能,以使用jQuery进行上传。功能从for循环中被调用了几次,所以我如何等待所有循环/ jquery调用完成,然后重定向?
function upload (photo, callback) {
var fd = new FormData();
fd.append('photo',photo);
return $.ajax({
url: 'upload.php',
type: 'post',
data: fd,
contentType: false,
processData: false,
success: function(response){
},
});
};
var completed = 0;
for (var i = 0; i < files.length; i++) {
upload(resizedFile, function (response) {
if (++completed == files.length) {
window.location = redirect_url;
}
});
}
promisify上传功能。使用JQuery会更短一些,因为$.ajax
返回一个可以转换的对象,但是使用老式的香草JS,它看起来像这样:
var upload = function (photo) {
return new Promise(function(resolve, reject) {
var request = new XMLHttpRequest();
request.onload = function() {
if (request.status >= 200 && request.status < 300) {
resolve(request.response);
} else {
reject(request.statusText);
}
};
request.onerror = function() { reject(request.statusText) }
request.open('POST', 'upload.php');
request.responseType = 'json';
var formData = new FormData();
formData.append('photo', photo);
request.send(formData);
})
}
另请参见:http://ccoenraets.github.io/es6-tutorial-data/promisify/然后我将这些诺言收集到一个数组中:
var uploads = files.map(function(file) { return upload(resizeFile(file)); })
(或简单地进行迭代,然后将它们放入数组中)然后您可以使用此代码来处理所有上载的完成:
Promise.all(uploads) .then(function(results) { /* do the redirect */ }) .catch(function(error) { console.log(error); });
另请参见:https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/all注:为什么在另一个答案中建议计数错误?因为当任何请求失败时,它不会处理条件。您将无法检测到这种情况,也永远无法达到满足的条件。承诺(和异步/等待)是处理异步操作(如ajax请求)的正确方法。
[更新]
这里是使用最新JS语言功能的JQuery方法:
var upload = (photo) => { photo = resizeFile(photo); let formData = new FormData(); formData.append('photo', photo); return $.ajax({ type: 'POST', url: 'upload.php', data: formData }) // check other the options of ajax method, you might need them } let uploads = files.map(upload); $.when.apply($,uploads) .done(_ => { /* do the redirect */ }) .fail(e => { /* handle error */ })
后一部分可以用async/await
语法编写:
async somefunction(){ // rest of the code try { await $.when.apply($,uploads) /* do the redirect */ } catch(ex) { /* handle error */ } }
注意,$.ajax
返回Deferred,它是与Promise兼容的JQuery对象。