I think this is better practice than parsing values directly into 'return'

You did it like a Boss!

you can return the string dirctly
return "text";

Why Object.assign(this, {firstName}) is used here instead of this.firstName=firstName? I haven't seen this method mentioned in a JavaScript book.

upd: copies into an object... Genius!

perfect examples of a simple problem solved with something that is really not worth trying to understand

Wouldn't this convert the full array to list first and then provide index of match?
why traverse through full array, when we can "return" upon finding the "needle" with a simple for loop, thoughts?

nice work

Aprendi algo nuevo, gracias a ti. Object.assign() ... Saludos de Salta,Argentina.

Someone can give me feedback about my solution?

Doesn't work if input parameter haystack=null. Need to add checking for null input.

Never thought about this, amazing!

Best practice is what people voted best practice. You must get used to it, and if you don't agree, you are free to vote for whatever you think is good practice.

why is this best practice? if statements are much more readable

Genius my friend , genius

I really like this . Its so clean !