From Callback To Async Await

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From Callback Hell To Async Await Tamar Twena-Stern

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Tamar Twena-Stern • Software Engineer - manager and architect • BackEnd Team Leader @XM Cyber • Was a CTO of my own startup • Passionate about Node.js ! • Twitter: @SternTwena

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Tamar Twena-Stern • Have 3 kids • Community Leader @JavaScript Israel • Loves to play my violin

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Traditional Approach - Blocking IO Client Server Request Request Request Thread Thread Thread

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Problems •CPU and memory resources location for every new thread and performs context switching •On stressed – Context switching over actual work

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Node.js Architecture - Non Blocking IO

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Asynchronous Programming • Synchronous activities will block the event loop. • Asynchronous programming has evolved in JavaScript • Functions are first class citizens • No return values, only function calls.

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Asynchronous Code Example

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So, why callbacks programming is so bad ?

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The Pyramid Of Doom

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Easy To Miss Error Handling

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Correct Error Handling

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Different To Implement Control Flows • Very hard to implement control flow patterns • You want to be able to execute tasks in : • Series • Parallel • Even implementing array mapping using pure asynchronous functions very hard with plane callbacks

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Promises

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What Is A Promise • A proxy for a value that we don’t know yet • Register an event handler to • Success of an asynchronous operation • Failure of an asynchronous operation • Enable an asynchronous method to return value like a synchronous method

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Promise - Explained

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Promises Code

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Promise Libraries • Native in ES6 • Bluebird – add a lot of extra functionality on native ES6 • Promise.mapSeries() • Promise.reduce() • Promise.map() • Promise.Some() • Promise.any() • Promise.each() • Etc …

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Lets Measure Some Performance

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Async Await

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What Is An Async Function • Return an Promise • Inside an async function, we can : • Use await before a function that returns a promise • Await waits for the promise to be resolved • Handle errors with easy and popular mechanism – try / catch • Behind the scenes – asynchronous code

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Await Keyword • Reserved word from ES7 • Can be used only inside an Async function • Await is used to wait for a promise • Await cause the execution of the function to stop • Same concept as generators • Help simplify the code to look synchronous • Behind the scenes – asynchronous code

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Some Async Await Code

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How The Situation Is Improved ?

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Concise And Clean • No need to use .than • No need to write anonymous callback function for .than or for .catch • Not creating variables that we will not need • Avoid nesting • Very intuitive

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Clear Error Handling

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Intermediate Values

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Parallel Execution Very Easy

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Watch Out • The code is very concise and clean • This is miss-leading as the biggest advantages of Node.js are • Non blocking IO • Parallel IO work with the worker thread pool • You have to remember to work as much in parallel as you can!