Write Better JavaScript with Promises

Promises make jQuery code easier to read because you can attach done, fail, and always handlers to the returned object, and the callbacks run in order. The article also shows that an API can return a promise instead of taking a handler, which makes it easier to pass the result around and transform it with then.

Reading notes

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• A callback example appends data.text to the page after a getJSON request succeeds.
• The promise version attaches done and fail handlers directly to the object returned by getJSON.
• jQuery also provides always, which runs whether the request succeeds or fails.
• The callback order is preserved, with done first, fail second, and always last.
• A wrapper around the HipsterJesus API can return a promise from html instead of accepting a handler.
• then can change the resolved value before passing it to the next handler in the chain.
• AngularJS once allowed templates to bind directly to promises, and the article says this feature was later deprecated.
• Promises can be chained to build small methods such as html, paragraphs, and sentences.
• Multiple API calls become simpler with $.when, which waits for both requests before running one handler.