gistfile1.js

/*
 * Truncate(string<String>, options<Object>, callback[Function])
 *
 * Truncates a given `string` after a specified `length` if `string` is longer than
 * `length`. The last characters will be replaced with an `omission` for a total length not
 * exceeding `length`. If `callback` is given it will fire if `string` is truncated.
 *
 * Options:
 *   length    <Integer>          Length the output string will be(default: 30)
 *   omission  <String>           Replace last letters with an omission(default: '...')
 *   ellipsis  <String>           Alias for omission
 *   seperator <String>/<RegExp>  Break the truncated text at the nearest `seperator`
 *
 * Warnings:
 *   Please be aware that truncating HTML tags or entities may result in malformed HTML returned
 *
 * Examples:
 *   truncate('Once upon a time in a world', { length: 10 })
 *   => 'Once upo...'
 *
 *  truncate('Once upon a time in a world', { length: 20, omission: '...(continued)' })
 *   => 'Once u...(continued)'
 *
 *  truncate('Once upon a time in a world', { length: 15, seperator: ' ' })
 *   => 'Once upon a...'
 *   Normal Output: => 'Once upon a ...'
 */
exports.truncate = {
  name: 'truncate',
  action: function(string, options, callback) {
    if(!string) return;
    options = options || {};

    // Set `options` defaults
    options.length = options.length || 30;
    options.omission = options.omission || options.ellipsis || '...';
    if(typeof options.escape === 'undefined') options.escape = true;

    var stringLen = string.length
      , stringLenWithOmission = options.length - options.omission.length
      , last;

    // Set the index to stop at for `string`
    if(options.seperator) {
      if(options.seperator instanceof RegExp) {
        // If `options.seperator` is a regex search
        if(options.seperator.global) {
          options.seperator = options.seperator;
        } else {
          var ignoreCase = options.seperator.ignoreCase ? 'i' : ''
            , multiLine = options.seperator.multiLine ? 'm' : '';

          options.seperator = new RegExp(options.seperator.source, 'g' + ignoreCase + multiLine);
        }
        var stringToWorkWith = string.substring(0, stringLenWithOmission + 1)
          , lastIndexOf = -1
          , nextStop = 0
          , result;

        while((result = options.seperator.exec(stringToWorkWith)) !== null) {
          lastIndexOf = result.index;
          options.seperator.lastIndex = ++nextStop;
        }
        last = lastIndexOf;
      } else {
        last = string.lastIndexOf(options.seperator, stringLenWithOmission);
      }

      // If the above couldn't be found, they'll default to -1 so, we need to just set
      // - it as `stringLenWithOmission`
      if(last === -1) last = stringLenWithOmission;
    } else last = stringLenWithOmission;

    if(stringLen < options.length) return string;
    return string.substring(0, last) + options.omission;
  }
};