Callbacks and control flow in Node js
- 1. ASYNCHRONOUS CODING IN NODEJS CALLBACKS AND CONTROL FLOW Thomas Roch, Formedix Ltd
- 3. WHAT IS NODEJS Node.js uses an event-driven, non-blocking I/O model that makes it lightweight and efficient, perfect for data-intensive real-time applications that run across distributed devices. Event driven => event listeners Non-blocking IO => callbacks = ASYNCHRONOUS
- 4. BEFORE WE START Non-blocking functions take callbacks (last argument) of two forms: function (err, res) { // Do something } function (res) { // Do something }
- 5. WE ARE GOING TO TALK ABOUT Callback hell Inversion of control Control flow Promises Thunks Generators (or iterators)
- 6. EXAMPLE A wish list server where one can: Create a whish list Add items to a whish list Retrieve the content of a whishlist Code available here
- 7. REST API POST /whishList POST /whishList/{id} GET /whishList/{id}
- 8. WHAT WE AIM FOR
- 9. WHAT WE ARE GOING TO DO FIRST
- 10. EXAMPLE A A mix of events and non-blocking functions with http.request() for: Creating a list Adding an item to a list Getting a list's content
- 11. EXAMPLE B: Turn this mess into functions accepting callbacks With 3 functions: createList, addItem, getList... ...we are creating a nice "callback hell" aka "callback pyramid"
- 12. ASYNC TO THE RESCUE First control flow example with https://github.com/caolan/async async.series() async.waterfall() async.parallel() Works with any non-blocking function "the node way"
- 13. OK... WE'VE DONE STUFF IN PARALLEL Does this look good? What about avoiding iversion of control?
- 14. EXAMPLE C: USING PROMISES ES6 feature but implementations available in ES5 Returns a deferred result (success or error) accessed using .then(): createList , addItem , getList Control flow using q : chaining promises, error propagation, Q.all... Compatible with Node API functions using Q.nfcall()
- 15. BEFORE EXAMPLE D Generators (or iterators)! What are they? function* () { yield 1; return 2; }
- 16. EXAMPLE D: USING GENERATORS What about yielding a promise or a thunk? a what? Control flow using co // The node way phoneMyPal(number, function (err, res) { console.log('hi'); }); // A thunk phoneMyPal(number)(function (err, res) { console.log('hi'); }); Let's thunkify createList, addItem, getList
- 17. EXAMPLE D: USING GENERATORS works with thunks or promises co Compatible with Node API using thunkify Non-blocking code looking like it is not! Used by koa.js , a web application framework
- 18. QUESTIONS