awesome-string/src/chop/truncate.js

The ultimate JavaScript string library

import clipNumber from 'helper/number/clip_number';
import coerceToString from 'helper/string/coerce_to_string';
import isNil from 'helper/object/is_nil';
import { MAX_SAFE_INTEGER } from 'helper/number/const';
import toInteger from 'helper/number/to_integer';

/**
 * Truncates `subject` to a new `length`.
 *
 * @function truncate
 * @static
 * @since 1.0.0
 * @memberOf Chop
 * @param  {string} [subject=''] The string to truncate.
 * @param  {int}    length       The length to truncate the string.
 * @param  {string} [end='...']  The string to be added at the end.
 * @return {string}              Returns the truncated string.
 * @example
 * as.truncate('Once upon a time', 7);
 * // => 'Once...'
 *
 * as.truncate('Good day, Little Red Riding Hood', 14, ' (...)');
 * // => 'Good day (...)'
 *
 * as.truncate('Once upon', 10);
 * // => 'Once upon'
 */
export default function truncate(subject, length, end) {
  const subjectString = coerceToString(subject);
  const lengthInt = isNil(length) ? subjectString.length : clipNumber(toInteger(length), 0, MAX_SAFE_INTEGER);
  const endString = coerceToString(end, '...');
  if (lengthInt >= subjectString.length) {
    return subjectString;
  }
  return subjectString.substr(0, length - endString.length) + endString;
}