Created
July 10, 2012 17:57
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createPromise() -- use promises with libraries that only support callback arguments
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var createPromise = function (wrapper) { | |
var deferred = $.Deferred(); | |
wrapper( | |
function () { deferred.resolve.apply(deferred, arguments); }, | |
function () { deferred.reject.apply(deferred, arguments); } | |
); | |
return deferred.promise(); | |
} | |
// USAGE: | |
// Say you have some old library that has success and fail callbacks rather than promises. | |
var asyncCalculator = { | |
add: function (a, b, success, fail) { | |
setTimeout(function () { | |
var result = a + b; | |
if (typeof result === 'number') { | |
if(success) success(result); | |
} else { | |
if (fail) fail(); | |
} | |
}, 1000); | |
} | |
}; | |
// The API expects you to pass two callback functions, one for success and one for failure | |
asyncCalculator.add( | |
5, | |
10, | |
function (result) { console.log('[callback] the sum is ' + result); }, | |
function () { console.log('[callback] could not add'); } | |
); | |
// We would prefer the function to return a promise. | |
var adding = asyncCalculator.add(5, 10); // <--- This doesn't work (adding is undefined). | |
// So wrap the call in createPromise(). It's a little extra boilerplate, but it works. | |
var adding = createPromise(function (success, fail) { | |
asyncCalculator.add(5, 10, success, fail); | |
}); | |
// Now we can pass around the promise and do whatever we like with it | |
adding.then(function (result) { | |
console.log('[promise] the sum is ' + result); | |
}, function () { | |
console.log('[promise] could not add'); | |
}); | |
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