awesome-string/src/manipulate/splice.js

The ultimate JavaScript string library

import coerceToNumber from 'helper/number/coerce_to_number';
import coerceToString from 'helper/string/coerce_to_string';

/**
 * Changes `subject` by deleting `deleteCount` of characters starting at position `start`. Places a new string
 * `toAdd` instead of deleted characters.
 *
 * @function splice
 * @static
 * @since 1.0.0
 * @memberOf Manipulate
 * @param {string} [subject=''] The string where to insert.
 * @param {string} start The position to start changing the string. For a negative position will start from the end of
 * the string.
 * @param {number} [deleteCount=subject.length-start] The number of characters to delete from string.
 * @param {string} [toAdd=''] The string to be added instead of deleted characters.
 * @return {string} Returns the modified string.
 * @example
 * as.splice('new year', 0, 4);
 * // => 'year'
 *
 * as.splice('new year', 0, 3, 'happy');
 * // => 'happy year'
 *
 * as.splice('new year', -4, 4, 'day');
 * // => 'new day'
 */
export default function splice(subject, start, deleteCount, toAdd) {
  const subjectString = coerceToString(subject);
  const toAddString = coerceToString(toAdd);
  let startPosition = coerceToNumber(start);
  if (startPosition < 0) {
    startPosition = subjectString.length + startPosition;
    if (startPosition < 0) {
      startPosition = 0;
    }
  } else if (startPosition > subjectString.length) {
    startPosition = subjectString.length;
  }
  let deleteCountNumber = coerceToNumber(deleteCount, subjectString.length - startPosition);
  if (deleteCountNumber < 0) {
    deleteCountNumber = 0;
  }
  return subjectString.slice(0, startPosition) + toAddString + subjectString.slice(startPosition + deleteCountNumber);
}