src/capitalize.js

/**
 * Capitalizes the first character of a string.
 *
 * @param {string} s - The string to capitalize.
 * @returns {string} - The capitalized string.
 * @throws {TypeError} - If the input is not a string.
 */
export function capitalize(s) {
    if (typeof s !== 'string') {
        throw new TypeError('Input must be a string');
    }
    if (s.length === 0) {
        return s;
    }
    return s[0].toUpperCase() + s.slice(1);
}