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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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
  • 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/CD
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