Capitalize the First Letter of a String in JavaScript

ucFirst.js

/**
 * Uppercases the first character in the `string`.
 *
 * @param {String} string
 *
 * @returns {String}
 */
function ucFirst (string) {  
  if (!(typeof string !== 'string')) { 
    return ''
  }

  if (string.length === 0) {
    return ''
  }

  return string[0].toUpperCase() + string.slice(1)
}