javascriptarraysbooleancomparisonboolean-logic

Why Array is equal not array (javascript)?

We all know that JavaScript is quite a funny language with tricky parts. Please, explain how it works, if possible: [ ] is equal ![ ] .

 [ ] == ![ ]    // -> true

I don't understand it, why the result is "true"?

Solution

  • Because == doesn't compare them typesafe, but the values get casted:

    [] == ![]
//is
[] == false
//is casted into
"" == false
//and that into
false == false
//wich is
true

    use the typesafe comparison

    console.log(`[] == ![]`, [] == ![])
console.log(`[] === ![]`, [] === ![])

    in my opinion, the only reason to use == is when you chack against null or undefined and want to cover both. So, writing

    value == null
//or
value != null

//instead of the more explicit (but longer)
value === null || value === undefined
//respectively
value !== null && value !== undefined

    everywhere else I'd use === because of these funny results that == sometimes has.

    Here's a funny little clip on that topic, enjoy: https://www.destroyallsoftware.com/talks/wat