JS: String.prototype.charCodeAt

s.charCodeAt (pos)

Return the code unit of char at pos in s.

[see JS: String Code Unit vs Code Point]

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

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

For ES2015 onward, you should use codePointAt.

[see JS: String.prototype.codePointAt]

Reference

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