showFirstAndLastFive.js

/**
 * Returns the first five characters followed by an ellipsis (...) and the last five characters of a given string.
 * If the string length is less than or equal to 10, the original string is returned.
 *
 * @param {string} str - The input string.
 * @returns {string} - The modified string with the first and last five characters, separated by an ellipsis.
 */
function showFirstAndLastFive(str) {
  // Check if the string length is less than or equal to 10
  if (str.length <= 10) {
    return str;
  }

  // Extract the first five characters from the string
  let firstFive = str.substr(0, 5);

  // Extract the last five characters from the string
  let lastFive = str.substr(str.length - 5);

  // Return the modified string with the first and last five characters, separated by an ellipsis
  return `${firstFive}...${lastFive}`;
}

function showFirstAndLastFive_test() {
  console.log(showFirstAndLastFive('Hello, world!')); // "Hello...orld!"
  console.log(showFirstAndLastFive('abcdefghijhiklmnopqrst')); // "abcde...pqrst"
  console.log(showFirstAndLastFive('a')); // "a"
}