lodash/internal/createComposer.js

define([], function() {

  /** Used as the `TypeError` message for "Functions" methods. */
  var FUNC_ERROR_TEXT = 'Expected a function';

  /**
   * Creates a function to compose other functions into a single function.
   *
   * @private
   * @param {boolean} [fromRight] Specify iterating from right to left.
   * @returns {Function} Returns the new composer function.
   */
  function createComposer(fromRight) {
    return function() {
      var length = arguments.length,
          index = length,
          fromIndex = fromRight ? (length - 1) : 0;

      if (!length) {
        return function() { return arguments[0]; };
      }
      var funcs = Array(length);
      while (index--) {
        funcs[index] = arguments[index];
        if (typeof funcs[index] != 'function') {
          throw new TypeError(FUNC_ERROR_TEXT);
        }
      }
      return function() {
        var index = fromIndex,
            result = funcs[index].apply(this, arguments);

        while ((fromRight ? index-- : ++index < length)) {
          result = funcs[index].call(this, result);
        }
        return result;
      };
    };
  }

  return createComposer;
});