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When To Use a Promise
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// ASSUME JQUERY | |
var document_cache = []; | |
function getDocument(documentId) { | |
var _deferred = new $.Deferred() | |
_document_sent = false; // Note that this could be removed by using `_deferred.state()` | |
; | |
// Iterate over the document_cache array | |
document_cache.forEach(function(thisDocument) { | |
// If the this is the document being asked for... | |
if (thisDocument.id == documentId) { | |
_document_sent = true; // Note that this could be removed by using `_deferred.state()` | |
// ...Send the document to the caller | |
_deferred.resolve(thisDocument); | |
} | |
}); | |
// If a document has not been sent... | |
if (!_document_sent) { // Note that this could also be done using `_deferred.state() == 'pending' ` | |
// ...try to get it from the API... | |
$.get('/path/to/document/api').done(function(fetchedDocument) { | |
// ...add it the document_cache for later use... | |
document_cache.push(fetchedDocument); | |
// ...and return it to the caller | |
_deferred.resolve(fetchedDocument); | |
}).fail(_deferred.reject); | |
} | |
// return our deffereds promise | |
return _deferred.promise(); | |
} | |
$('a.document').on('click', function(e) { | |
e.preventDefault(); | |
var _working = $("<span>").html("Working Icon"); | |
$(this).append(_working); | |
// Call our getDocument Function | |
getDocument($(this).text()).done(function(thisDocument) { | |
// alert out our selected document | |
alert(thisDocument); | |
}).fail(function(error) { | |
// alert that an error occured | |
alert(error); | |
}).always(function() { | |
// no matter what, remove the working "icon" | |
_working.remove(); | |
}); | |
}); |
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