lodash/_createPadding.js

define(['./_baseRepeat', './_stringSize', './_stringToArray'], function(baseRepeat, stringSize, stringToArray) {

  /** Used as a safe reference for `undefined` in pre-ES5 environments. */
  var undefined;

  /** Used to compose unicode character classes. */
  var rsAstralRange = '\\ud800-\\udfff',
      rsComboMarksRange = '\\u0300-\\u036f\\ufe20-\\ufe23',
      rsComboSymbolsRange = '\\u20d0-\\u20f0',
      rsVarRange = '\\ufe0e\\ufe0f';

  /** Used to compose unicode capture groups. */
  var rsZWJ = '\\u200d';

  /** Used to detect strings with [zero-width joiners or code points from the astral planes](http://eev.ee/blog/2015/09/12/dark-corners-of-unicode/). */
  var reHasComplexSymbol = RegExp('[' + rsZWJ + rsAstralRange  + rsComboMarksRange + rsComboSymbolsRange + rsVarRange + ']');

  /* Built-in method references for those with the same name as other `lodash` methods. */
  var nativeCeil = Math.ceil;

  /**
   * Creates the padding for `string` based on `length`. The `chars` string
   * is truncated if the number of characters exceeds `length`.
   *
   * @private
   * @param {number} length The padding length.
   * @param {string} [chars=' '] The string used as padding.
   * @returns {string} Returns the padding for `string`.
   */
  function createPadding(length, chars) {
    chars = chars === undefined ? ' ' : (chars + '');

    var charsLength = chars.length;
    if (charsLength < 2) {
      return charsLength ? baseRepeat(chars, length) : chars;
    }
    var result = baseRepeat(chars, nativeCeil(length / stringSize(chars)));
    return reHasComplexSymbol.test(chars)
      ? stringToArray(result).slice(0, length).join('')
      : result.slice(0, length);
  }

  return createPadding;
});