{"id":3171,"date":"2017-12-20T20:16:54","date_gmt":"2017-12-20T14:46:54","guid":{"rendered":"https:\/\/code4developers.com\/?p=3171"},"modified":"2017-12-20T20:19:02","modified_gmt":"2017-12-20T14:49:02","slug":"programming-asynchronously-promises","status":"publish","type":"post","link":"https:\/\/code4developers.com\/programming-asynchronously-promises\/","title":{"rendered":"Programming asynchronously: Promises"},"content":{"rendered":"

Promises are in many ways the logical next step from callback. A promise is just a special object that promise to either resolve, or throw an exception.
\nPromises are easy to use, and easy to make. For example this is how you use some kind of library that uses promises:<\/p>\n

function(params)\r\n.then(response=>{\/*method to deal with the response*\/})\r\n.catch(e=>{\/* method to deal with the exception*\/})<\/pre>\n
You can also run multiple promises at once, with the Promise.all() method; useful when you have to load a lot of different stuff, like for example when your app starts and you need to load a lot of stuff into redux \/ state. And you can chain the thens as long as you return a response in the one before it.
\nBut the thing that is important to remember is that a promise will no do anything before you call .then() on it.
\nAnd this is how you define a promise:<\/p>\n
new Promise(function(resolve, reject){\r\n  let data = myAwesomeMethod()\r\n  if(data) resolve(data)\r\n  else reject(data)\r\n})<\/pre>\n
There are also tools like bluebird<\/a> that can \u2018promisify\u2019 callback based methods.
\nI think Promises are awesome, for a number of reasons. They formalize things much more than a callback based api does. And I personally think that Promise.all makes it much easier to avoid callback hell.<\/p>\n","protected":false},"excerpt":{"rendered":"
Promises are in many ways the logical next step from callback. A promise is just a special object that promise to either resolve, or throw an exception.<\/p>\n","protected":false},"author":7,"featured_media":3127,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[2],"tags":[87,22,80,84,85,86],"powerkit_post_featured":[],"class_list":{"0":"post-3171","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-javascript","8":"tag-bluebirdjs","9":"tag-javascript","10":"tag-node","11":"tag-programming-asynchronously","12":"tag-promises","13":"tag-promisify"},"jetpack_featured_media_url":"https:\/\/i0.wp.com\/code4developers.com\/wp-content\/uploads\/2017\/10\/javascript.jpg?fit=750%2C422&ssl=1","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p8NAi4-P9","jetpack-related-posts":[{"id":3169,"url":"https:\/\/code4developers.com\/programming-asynchronously-async-await\/","url_meta":{"origin":3171,"position":0},"title":"Programming asynchronously: Async Await","author":"Arif Khoja","date":"December 19, 2017","format":false,"excerpt":"One of the big issues with using either callbacks or Promises is that the code becomes much more complex that it would, if you were using a synchronous programming language. 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The keywords are borrowed from C# and .NET and is without doubt\u2026","rel":"","context":"In "JavaScript"","block_context":{"text":"JavaScript","link":"https:\/\/code4developers.com\/category\/javascript\/"},"img":{"alt_text":"javascript","src":"https:\/\/i0.wp.com\/code4developers.com\/wp-content\/uploads\/2017\/10\/javascript.jpg?fit=750%2C422&ssl=1&resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/code4developers.com\/wp-content\/uploads\/2017\/10\/javascript.jpg?fit=750%2C422&ssl=1&resize=350%2C200 1x, https:\/\/i0.wp.com\/code4developers.com\/wp-content\/uploads\/2017\/10\/javascript.jpg?fit=750%2C422&ssl=1&resize=525%2C300 1.5x, https:\/\/i0.wp.com\/code4developers.com\/wp-content\/uploads\/2017\/10\/javascript.jpg?fit=750%2C422&ssl=1&resize=700%2C400 2x"},"classes":[]},{"id":3174,"url":"https:\/\/code4developers.com\/for-of-loop\/","url_meta":{"origin":3171,"position":1},"title":"For-of Loop","author":"Arif Khoja","date":"December 25, 2017","format":false,"excerpt":"For of loop is one of a few recent additions to the for loop in JavaScript. 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