Function isHighSurrogate

src/utils/characters.ts:7–13

(string: string, index = 0)

const HEX_DIGIT = /^[0-9a-fA-F]$/;

export function isHighSurrogate(string: string, index = 0): boolean {
	if (index < 0 || index >= string.length) {
		return false;
	}
	const charCode = string.charCodeAt(index);
	return charCode >= MIN_HIGH_SURROGATE && charCode <= MAX_HIGH_SURROGATE;
}

export function isLowSurrogate(string: string, index = 0): boolean {
	if (index < 0 || index >= string.length) {