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"?
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Because array in JavaScript is an object. See Mozilla CDN Arraysomurbek– omurbek2017-08-16 07:37:00 +00:00Commented Aug 16, 2017 at 7:37
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2 Answers
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
2 Comments
Yurii Savchuk
Thomas, thanks for answers. I review some crazy examples and try to understand how they work. Now I understand this example.
evolutionxbox
@YuriiSavchuk for more info, research into truthy and falsy values.
When you call if (array == false) you compare values of this object and the primitive false value. Internally, arr.toString() is called, which returns an empty string "".
![] // will return false
[] == false // this would return true, since "" == false
console.log((![]).toString());
console.log(([]).toString());
console.log("" == false);This is how it is called internally, please check out this answer for more details
1 Comment
Yurii Savchuk
marvel308, thanks for answers. I review some crazy examples and try to understand how they work. Now I understand this example.