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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