JavaScript promises, mastering the asynchronous


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You are now towards the end of this playground. However, the wild outside can be dangerous. So don't leave without a few tricks!

Test if an object is a promise

If you really have to, this is how you can test if an object is a promise : obj instanceof Promise. The problem is that this test only works with a real Promise object. It will not work with the Q library or with an Angular promise.


Promise.race takes an array of promises. The result is a new promise that resolves or rejects as soon as one of the promises in the given array resolves or rejects.

Promise.race example
function delay(time) {
return new Promise(function(resolve) {
setTimeout(resolve, time, 'success ' + time);
Promise.race([delay(500), delay(100)]).then(function(data) {
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