Quick and easy way of counting UTF-8 characters in Javascript

18 Jun 18 20:00
2 minutes read

Reading the following tutorial regarding a VueJS component that displays the character count for a textarea got me thinking.

You see, the problem is that when Javascript was first created it didn’t had proper UTF-8 support. Javascript’s internal encoding is UCS-2 or UTF-16 depending the articles you find on the internet. (actually there’s an awesome article from 2012 that explains this in detail ) .

What does that mean you say ? Well it’s rather straightforward, if you’re trying to get the length property of a string that contains UTF-8 3/4 byte (that translate into UTF-16 surrogate pair characters) your length will return 2 for each of the characters.

This might not be an issue usually, but it’s a big issue if you’re having a password policy of 8 characters that can be filled by just 4 “😹🐶😹🐶” (ok, not the best example, but everybody likes cats and dogs)

let lengthTest = "😹🐶😹🐶";
// will display 8

Now the fix with modern Javascript is rather easy, because it supports surrogates properly in arrays, and using array destructuring makes it a quick and easy one liner.

let lengthTest = "😹🐶😹🐶";
// will display 4

I’m interested in knowing if you got any weird/interesting experiences with UTF-8

PS: Use this link for a nice simple-ish explanation of Unicode encodings

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