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Filtering Punctuation from an Array (what is the exclamation ‘!’ doing?)

In example 1, the exclamation (!) is at the start of the punctuation array and does not get logged.

JavaScript

In example 2, the exclamation is somewhere else in the punctuation array and now gets logged.

JavaScript

I believe it’s being interpreted as a logical-not-operator but I’m unsure why since I would assume the quotation marks would make it a string.

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Answer

Instead of punctuation.indexOf(letter) > 0 you shall use punctuation.indexOf(letter) >= 0 or better punctuation.includes(letter).

If you use > instead of >= the first element which has index 0 would get excluded. And nevertheless indexOf returns -1 for non existing elements, not 0.

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