Surrogates.tsx

/**
 * Check if a code unit forms part of a surrogate pair. Surrogate pairs are rendered as one character but stored
 * as two characters in a JS string.
 * https://dmitripavlutin.com/what-every-javascript-developer-should-know-about-unicode/#24-surrogate-pairs
 */
const isSurrogate = (code: number): boolean => 0xd800 <= code && code <= 0xdfff;

/* Modify our onKeyDown Backspace Handler slightly... */
if (e.keyCode === Keycodes.BACKSPACE) {
	if (start === 0) return;
	const charsToRemove = isSurrogate(value.charCodeAt(start - 1)) ? 2 : 1;
	return insertString("", { start: start - charsToRemove, end: start });
}