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!
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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
- 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
- We only have numbers in TS, no floats/ints
- We do have BigInt though, but not something most people will use
- Will be a list of another type
- This type will be one of the possible options
- String of DRAFT PUBLISHED or ARCHIVED
- An intersection type combines multiple types into one
- These are custom types where each property is its own type
- Explicit any
- Implicit any
- Language types
- These things are technically just Objects, but they have their own types
- DOM Elements / Nodes
- When a function returns nothing — usually used with side effects like click handlers
- 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
- A set of named constants
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
- 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
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/CD
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