In this episode of Syntax, Scott and Wes talk about TypeScript fundamentals — what it is, how you use it, why people love it so much, and more! Sanity - Sponsor Sanity.io is a real-time headless CMS with a fully customizable Content Studio built in React. Get a Sanity powered site up and running in minutes at sanity.io/create. Get an awesome supercharged free developer plan on sanity.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. Cloudinary - Sponsor Cloudinary is the best way to host, compress and transform your images on the web. Sign up for their free tier and get 10GB of bandwidth for free! Show Notes What is TypeScript? 03:12 - Types? What are types and why should you care? JS is a typed language, it’s just not strongly typed JS does not care about reassignment of a variable to a new type Does not care about your types, but they do exist 06:34 - The Fundamentals You write your JavaScript code, but each time you create a variable, function, parameter, you “type it” — which means you describe what that data will look like. Create a variable: Will it be a string? A number? A custom type of show? Create a function: What params does it take? What type are they? What does it return? Types allow your code to know if there are type errors that would present themselves to the user silently. These are small errors that can be compounded and go unnoticed. This can allow you to prevent shipping code that has these errors by checking your code. Some of the biggest benefits here come via errors in your text editor 13:30 - Explaining the types You can create your own types Strings Numbers We only have numbers in TS, no floats/ints We do have BigInt though, but not something most people will use Arrays Will be a list of another type Unions This type will be one of the possible options String of DRAFT PUBLISHED or ARCHIVED Intersections An intersection type combines multiple types into one Objects These are custom types where each property is its own type Any Explicit any Implicit any Language types These things are technically just Objects, but they have their own types Dates Timeouts DOM Elements / Nodes Void When a function returns nothing — usually used with side effects like click handlers Enum A set of named constants Used when you have a select amount of values — I like to think of these as the select lists of TS String unions are also used for this same thing 30:28 - Inference Automatic detection of types Typescript will try to infer your types based on their definition Not every type can be inferred, leading to implicit anys and the need for explicit types 33:25 - Getting types Most popular packages already have types — you install them like npm i @types/whatever If a package doesn’t have types, you have to create them yourself, which can be annoying MakeTypes Console log a JSON.stringify(obj), and pipe it in Node has types Vanilla JS has types, for the language and all of the DOM - HTMLInputElement React has types Typing Node modules that don’t have types Overall benefits 40:39 - Type hinting With TS and your editor (VSCode) you’ll get more information about your code as you type it — allowing you to know exactly what things expect This seems like a small deal but in practice leads to being much more efficient 42:50 - Refactoring Rename a function, type, or variable and it will be updated everywhere in the project! Moving a function to a new file is actually part of TypeScript Drag + Drop file, update imports 48:10 - Compiling TSC vs Babel / Esbuild Only TSC type checks Compiling TS with babel will not allow you to break the build on type errors, you’ll need to run TSC in coordination or in the CI/