TypeScript Fundamentals

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

• 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

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

• Snipcart
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• Wes: Phomemo Label Printer

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