StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

POChain promises and break out on error WinJS
primarykey
Id
13709739
data
AcceptedAnswerId
13713115
AnswerCount
3
ClosedDate
CommentCount
0
CommunityOwnedDate
CreationDate
2012-12-04T18:43:19.653
FavoriteCount
0
LastActivityDate
2016-04-07T09:30:32.377
LastEditDate
2012-12-05T08:02:03.087
LastEditorUserId
597384
OwnerUserId
597384
ParentId
0
PostTypeId
1
Score
1
ViewCount
1860
LastEditorDisplayName
text
Body
In WinJS, what is the correct way to chain promises if you needed to "break out" of the chain? For instance, if you had .then() functions and a final .done(). What is the correct way to return an error from a then that has others after it? Consider the following pseudo-code example <pre><code> function doSomething(){ return new WinJS.Promise(function(comp,err,prog){ filePicker.pickSingleFileAsync().then(function(file){ if(file){ // have a valid file return readTextAsync(File); }else{ //else user clicked cancel return err('No file'); } }).then(function(text){ if(text){ return comp(text); }else{ return err('No text'); } }).done(null, function(error){ //final done to catch errors return err(error); }); });// end return promise } //end doSomething(); doSomething().done(function(text){ console.log(text); }, function(err){ console.log(err); }); </code></pre> Now in this simplified example, if a user cancels the filePicker, they should hit the first err("No File"); however this still proceeds to call the next .then(text) which would also return an error('no text') as text is undefined. The overall doSomething().done() error handler returns "No File" here which is what I would expect, but debugging shows the code still calls the "err('No Text')" part of the promise. Is it possible to actually exit the promise chain at this point? Should I look at using the <a href="http://msdn.microsoft.com/en-gb/library/windows/apps/br229660.aspx" rel="nofollow">any</a> method here some how? thanks ***EDIT . In case others want to know what my solution looked like based on the accepted answer below it is as follows: <pre><code> filePicker.pickSingleFileAsync().then(function (file) { if (file) { return Windows.Storage.FileIO.readTextAsync(file); } return WinJS.Promise.wrapError("No File"); }).then(function (text) { if (text) { return complete(text); } return error("no text"); }).done(null, function (err) { return error(err); }); </code></pre>
Tags
<winjs><promise>
Title
Chain promises and break out on error WinJS
singulars
PostAcceptedAnswerId
1. PO
 singulars
 PostTypePostTypeId
 PTAnswer
PostParentId
1. This table or related slice is empty.
PostTypePostTypeId
1. PTQuestion
UserLastEditorUserId
1. USTommyBs
UserOwnerUserId
1. USTommyBs
plurals
PostLinksPostIdRelatedPostId
1. This table or related slice is empty.
PostLinksRelatedPostIdPostId
1. PL
 singulars
 LinkTypeLinkTypeId
 LTLinked
PostsAcceptedAnswerId
1. This table or related slice is empty.
PostsParentIdCreationDate
1. PO
 singulars
 PostTypePostTypeId
 PTAnswer
2. PO
 singulars
 PostTypePostTypeId
 PTAnswer
VotesPostIdCreationDate
1. This table or related slice is empty.
CommentsPostId
1. This table or related slice is empty.

Querying!

Guidance

A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.