filter-limitTo.js

(function() {

  function isArray(value) {
    return toString.call(value) === '[object Array]';
  }
  function isString(value){return typeof value === 'string';}

  function int(str) {
    return parseInt(str, 10);
  }

  /**
   * Creates a new array or string containing only a specified
   * number of elements. The elements are taken from either
   * the beginning or the end of the source array or string,
   * as specified by the value and sign (positive or negative) of `limit`
   *
   * Note: this is a straight-up port from the Angular limitTo filter
   * and they deserve full credit for the implementation.
   * @param  {Array|string} input input Source array or string to be limited.
   * @param  {string|number} limit The length of the returned array or string. If the `limit` number
   *     is positive, `limit` number of items from the beginning of the source array/string are copied.
   *     If the number is negative, `limit` number  of items from the end of the source array/string
   *     are copied. The `limit` will be trimmed if it exceeds `array.length`
   * @return {Array|string} A new sub-array or substring of length `limit` or less if input array
   *     had less than `limit` elements.
   */
  PolymerExpressions.prototype.limitTo = function(input, limit) {

      if (!isArray(input) && !isString(input)) return input;

      limit = int(limit);

      if (isString(input)) {
        //NaN check on limit
        if (limit) {
          return limit >= 0 ? input.slice(0, limit) : input.slice(limit, input.length);
        } else {
          return "";
        }
      }

      var out = [],
        i, n;

      // if abs(limit) exceeds maximum length, trim it
      if (limit > input.length)
        limit = input.length;
      else if (limit < -input.length)
        limit = -input.length;

      if (limit > 0) {
        i = 0;
        n = limit;
      } else {
        i = input.length + limit;
        n = input.length;
      }

      for (; i<n; i++) {
        out.push(input[i]);
      }

      return out;
    };
})();