[英]Using promises to execute ajax synchronously
這是我處理文件上傳的代碼:
但是因為我沒有使用promises,所以它沒有以正確的順序運行! 當我上傳多個文件時,代碼的ajax部分在最后運行(我正在使用krajee bootstrap並且此代碼執行實際的文件上傳!)。 這是代碼:
$('#uploadNoteImage').on('fileloaded', function (event, file, previewId, index, reader) {
var url = noTrailingSlash(window.location.href) + '/user/notes';
console.log("1) Notes upload number: "+index);
var imgpgno = parseInt(getNotesLength(noteTitle, notesData));
console.log("2) Got page number of image "+imgpgno);
var data = {
"subject": noteTitle,
"pgno": imgpgno + 1,
"note": reader.result
};
console.log("3) Formed data object:");
console.log(data);
$.ajax({
url: url,
method: "PUT",
data: data,
success: function (data) {
console.log("4) Successfully uploaded data");
console.log(data);
toastr.success('', 'Added!');
var order = getIndexToDelete(noteTitle, notesData);
console.log("5) Fetched order number: "+order);
var id = Math.floor(Math.random() * 1000);
if (imgpgno == 0) {
console.log("6)(No notes uploaded yet state) Images before uploading"+images);
modalImg.src = reader.result;
notesData[order].data.push({
"id": id, "pgno": imgpgno + 1,
"note": reader.result
});
images = imgpgno + 1;
console.log("7)(No notes uploaded yet state) Images after uploading: "+images);
// imgpgno++;
}
else if(imgpgno!=0) {
var newPageNo=imgpgno + 1;
console.log("6)(1 note uploaded state) Pushing data with pgno: "+newPageNo);
notesData[order].data.push({
"id": id, "pgno": newPageNo,
"note": reader.result
});
images = imgpgno + 1;
console.log("7)(1 note uploaded state) Images after uploading: "+images);
}
},
error: function (err) {
toastr.error('Try again!', 'Something went wrong in uploading note!');
console.log(err);
}
});
});
我如何在這里包含promises,以便代碼以正確的順序運行? 我在這里詳細概述了這個問題: AJAX代碼的延遲執行
最簡單的方法需要一點點“設置” -
var uploadInProgress = $.when();
這將“填充” uploadInProgress
變量,以便第一次上傳將在我們希望的時候開始
整個代碼與您已有的代碼差別不大:
var uploadInProgress = $.when();
$('#uploadNoteImage').on('fileloaded', function (event, file, previewId, index, reader) {
// here, we chain the "pending" upload to this one
uploadInProgress = uploadInProgress.then(function() {
var url = noTrailingSlash(window.location.href) + '/user/notes';
console.log("1) Notes upload number: "+index);
var imgpgno = parseInt(getNotesLength(noteTitle, notesData));
console.log("2) Got page number of image "+imgpgno);
var data = {
"subject": noteTitle,
"pgno": imgpgno + 1,
"note": reader.result
};
console.log("3) Formed data object:");
console.log(data);
return $.ajax({
url: url,
method: "PUT",
data: data
// since we are using Promise pattern, use .then for success, and .catch for error conditions
}).then(function (data) {
console.log("4) Successfully uploaded data");
console.log(data);
toastr.success('', 'Added!');
var order = getIndexToDelete(noteTitle, notesData);
console.log("5) Fetched order number: "+order);
var id = Math.floor(Math.random() * 1000);
if (imgpgno == 0) {
console.log("6)(No notes uploaded yet state) Images before uploading"+images);
modalImg.src = reader.result;
notesData[order].data.push({
"id": id, "pgno": imgpgno + 1,
"note": reader.result
});
images = imgpgno + 1;
console.log("7)(No notes uploaded yet state) Images after uploading: "+images);
// imgpgno++;
}
else { // if(imgpgno!=0) { // the check is redundant since when the above if condition is false, this has to be true
var newPageNo=imgpgno + 1;
console.log("6)(1 note uploaded state) Pushing data with pgno: "+newPageNo);
notesData[order].data.push({
"id": id, "pgno": newPageNo,
"note": reader.result
});
images = imgpgno + 1;
console.log("7)(1 note uploaded state) Images after uploading: "+images);
}
}).catch(function (err) {
// this catch ensures that the next upload will be able to run regardless of this upload's failure
toastr.error('Try again!', 'Something went wrong in uploading note!');
console.log(err);
});
});
});
取而代之的是的success:
/ error:
回調,使用的事實, $.ajax
返回一個Promise
,和使用.then
/ .catch
-這使得它很容易鏈上傳后,其他請求一個
注意:確保.catch實際上處理錯誤(即不拋出一個)或者promise鏈將破壞 - 你error:
的代碼error:
很好,因為它是
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