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Wes Bos

Wes Bos

Full Stack JavaScript Developer. Creator of really good web development courses. BBQ enthusiast.

Scott Tolinski

Scott Tolinski

Web Developer, Creator of Level Up Tuts, Bboy, Robotops Crew and Youtuber

Playing: 324: TypeScript Fundamentals

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Feb 3rd, 2021

TypeScript Fundamentals

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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
    • 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/CD

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