A Tasty Treats Podcast for Web Developers.

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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: 317: Hasty Treat - A Podcast About Nothing

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LOUDNESS

Jan 11th, 2021

Hasty Treat - A Podcast About Nothing

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In this Hasty Treat, Scott and Wes talk about nothing — null, undefined, void, false, 0, '', NaN, [], {}, never — all sorts of values that could mean the things that do not exist.

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Show Notes

03:35 - Undefined

  • Implicitly nothing
  • A variable declared, but not set is undefined

04:25 - Null

  • Explicitly nothing

04:41 - Null vs Undefined

  • Null has a value of nothing
  • Undefined does not have a value
  • You can set variables to either
    • If you want to set a score variable to nothing, set it to null
    • If you want to un-set a value, set it to undefined
    • == will check if a value is either null or undefined

05:35 - Void

  • In Javascript
    • You can pop void in front of calling a function and it will return undefined (even if that function returns a value)
    • I've seen it on links that go nowhere (don't do this — use a button)
    • To prevent an arrow function from leaking
    • onSubmit="javascript:void()" is a quick-n-easy prevent default on forms
  • In Typescript
    • Void is when you don’t care about what is returned from a function, or if nothing is returned
    • A click handler that goes off and does stuff (side effect) can return void

09:15 - Never (in Typescript)

  • Some functions will never return:
    • Functions that throw errors
    • Functions that have infinite loops
    • Also, unreachable variables have a type of never
      • if(true == false) { let var = 'this will never be true'; }

11:05 - Falsy values

  • 0, -0, 0n
  • false
  • '' (empty string)
  • Empty array
    • Is a value
    • Its .length can be falsy
  • Empty object
    • Is a value
    • Its object.keys(object) length can be falsy (0)

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