unicorn/prefer-code-point

charCodeAt() and String.fromCharCode() work in 16-bit units. Emoji and many other characters take two units. For those, charCodeAt(0) returns the number of half a character, and String.fromCharCode(0x1F600) drops the high bits and returns a different character. codePointAt() and String.fromCodePoint() handle the whole character.

--fix-dangerously renames the method. --fix doesn't, because the result changes for those characters.

Configure

Off by default. To turn it on:

[lint.rules]
"unicorn/prefer-code-point" = "error" # or "warn"

Examples

Reported:

const code = text.charCodeAt(0);
const letter = String.fromCharCode(code);

Not reported:

const code = text.codePointAt(0);
const letter = String.fromCodePoint(code);

When not to use it

Code that works on UTF-16 units on purpose, such as an encoder or a hash that must match another implementation, needs charCodeAt().