Dive into the intriguing world of JavaScript as the hosts explore the elusive concepts of null, undefined, and void. Discover how to differentiate between these values and their proper uses in programming. Unravel the mysteries of TypeScript’s ‘never’ type and learn about various falsy values that can trip up developers. Plus, get insights into managing empty strings and objects effectively. It's a fun and informative discussion about the many ways nothingness plays a crucial role in coding!
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insights INSIGHT
Undefined vs. Null
Undefined means a variable exists but has no assigned value.
It's implicitly nothing, unlike null, which is explicitly nothing.
insights INSIGHT
Null vs. Undefined
Null is explicitly nothing; you assign it.
Undefined means a variable hasn't been assigned a value.
volunteer_activism ADVICE
Using Null and Undefined
Use null to intentionally set a variable to nothing (like a score).
Use undefined to unset a variable, returning it to its original state.
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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'; }
Syntax - Tasty Web Development Treats