JS: String.prototype.charCodeAt

s.charCodeAt (pos)

Return the code unit of char at pos in s.

[see JS: Character, Code Unit, Code Point]

If this character has Unicode codepoint less than 2^16, then, result is identical to s.codePointAt(pos).

// char “a” has codepoint 97
console.log ( "abc".charCodeAt (0) === 97 );
// true

Note, you probably want codePointAt instead.

[see JS: String.prototype.codePointAt]

Reference

ECMAScript 2015 §Text Processing#sec-string.prototype.charcodeat