In this Hasty Treat, Scott and Wes talk about nothing — null, undefined, void, false, 0, ‘’, NaN, [], {}, never — all sorts of values that could mean the things that do not exist. Prismic - Sponsor Prismic is a Headless CMS that makes it easy to build website pages as a set of components. Break pages into sections of components using React, Vue, or whatever you like. Make corresponding Slices in Prismic. Start building pages dynamically in minutes. Get started at prismic.io/syntax. LogRocket - Sponsor LogRocket lets you replay what users do on your site, helping you reproduce bugs and fix issues faster. It’s an exception tracker, a session re-player and a performance monitor. Get 14 days free at logrocket.com/syntax. Show Notes 03:35 - Undefined Implicitly nothing A variable declared, but not set is undefined 04:25 - Null Explicitly nothing 04:41 - Null vs Undefined Null has a value of nothing Undefined does not have a value You can set variables to either If you want to set a score variable to nothing, set it to null If you want to un-set a value, set it to undefined == will check if a value is either null or undefined 05:35 - Void In Javascript You can pop void in front of calling a function and it will return undefined (even if that function returns a value) I’ve seen it on links that go nowhere (don’t do this — use a button) To prevent an arrow function from leaking onSubmit="javascript:void()" is a quick-n-easy prevent default on forms In Typescript Void is when you don’t care about what is returned from a function, or if nothing is returned A click handler that goes off and does stuff (side effect) can return void 09:15 - Never (in Typescript) Some functions will never return: Functions that throw errors Functions that have infinite loops Also, unreachable variables have a type of never if(true == false) { let var = 'this will never be true'; } 11:05 - Falsy values 0, -0, 0n false ‘’ (empty string) Empty array Is a value Its .length can be falsy Empty object Is a value Its object.keys(object) length can be falsy (0) Tweet us your tasty treats! Scott’s Instagram LevelUpTutorials Instagram Wes’ Instagram Wes’ Twitter Wes’ Facebook Scott’s Twitter Make sure to include @SyntaxFM in your tweets