jQuery Deferred: Rejecting a Promise from within a Done Filter
In jQuery (unlike some other libs), transmogrifying a promise from a 'resolved' state to an 'rejected' state is slightly verbose, requiring the explicit creation and rejection of a new Deferred.
function foo() {
return doAJAXRequest().then(function (data, textStatus, jqXHR) {
if (data.responseText == "YES") {
return doOtherAJAXRequest(data);
} else {
return $.Deferred().reject(jqXHR, data, 'Not YES').promise();
}
});
)
Here, the promise returned if data.responseText !== "YES"
mimics (in part) a failed ajax request, while still allowing data
to be passed. This is (probably) important for the downstream .fail()
handler, which must handle both genuine ajax failures AND transmogrified success conditions, without knowing which one occurred until it reads errorThrown
.
foo().fail(function(jqXHR, textStatus, errorThrown) {
if(errorThrown == 'Not YES') {
//transmogrified success
var data = textStatus;
...
}
else {
//genuine ajax failure
...
}
});
It is generally easier to pass data
in this way rather than re-obtaining it from the jqXHR object. This is particularly true with JSON encoded data, which would otherwise need to be decoded a second time in the fail handler.
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Ajedi32
Full stack web developer/Linux admin/DevOps guy with experience in a broad range of topics including Ruby on Rails, Docker, Bash, JavaScript, PowerShell, git, etc.
Updated on June 04, 2022Comments
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Ajedi32 about 2 years
Fyi, I'm just starting to learn jQuery promises, so I may be a bit confused here.
Anyway, I have an AJAX request that I want to reject from within a done filter based on the content of the response:
return doAJAXRequest().then(function (data) { if (data.responseText == "YES") { return doOtherAJAXRequest(); } else { this.reject(data); } });
That didn't work as I expected:
Uncaught TypeError: Object #<Object> has no method 'reject'
How do I make this promise fail based on its response? Is that possible? Or am I just confused about what needs to be done here?
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rtimoshenko almost 11 yearsMy mistake, I saw "this" and made an assumption. Have you compared your code with the documentation? api.jquery.com/deferred.then You might try using the global $.Deferred().reject. Here's a jsFiddle: jsfiddle.net/pgBCD
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Ajedi32 almost 11 years@rtimoshenko Well, this seems to work: jsfiddle.net/pgBCD/1
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mikus about 8 yearsI don't think the promise() part is needed (or not anymore), which makes the call a bit less ugly/longish.