How do I reverse `String.fromCodePoint`, i.e. convert a string to an array of code points?

Question

String.fromCodePoint(...[127482, 127480]) gives me a flag of the US ().

How do I turn the flag back to [127482, 127480]?

Answer 1

You're looking for codePointAt, perhaps using spread (etc.) to convert back to array and then mapping each of them.

console.log(theString.codePointAt(0)); // 127482
console.log(theString.codePointAt(2)); // 127480
// Note −−−−−−−−−−−−−−−−−−−−−−−−−−^
// It's 2 because the first code point in the string occupies two code *units*

or

const array = [...theString].map(s => s.codePointAt(0));
console.log(array); // [127482, 127480]

or skipping an interim step as Sebastian Simon pointed out via Array.from and its mapping callback:

const array = Array.from(theString, s => s.codePointAt(0));
console.log(array); // [127482, 127480]

Example:

const theString = String.fromCodePoint(...[127482, 127480]);

console.log(theString.codePointAt(0)); // 127482
console.log(theString.codePointAt(2)); // 127480

const array = [...theString].map(s => s.codePointAt(0));
console.log(array);  // [127482, 127480]

const array2 = Array.from(theString, s => s.codePointAt(0));
console.log(array2); // [127482, 127480]

Spread and Array.from both work by using the strings iterator, which works by code points, not code units like most string methods do.