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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