function/flow.js

define(['../internal/arrayEvery', '../lang/isFunction'], function(arrayEvery, isFunction) {

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

  /**
   * Creates a function that returns the result of invoking the provided
   * functions with the `this` binding of the created function, where each
   * successive invocation is supplied the return value of the previous.
   *
   * @static
   * @memberOf _
   * @category Function
   * @param {...Function} [funcs] Functions to invoke.
   * @returns {Function} Returns the new function.
   * @example
   *
   * function add(x, y) {
   *   return x + y;
   * }
   *
   * function square(n) {
   *   return n * n;
   * }
   *
   * var addSquare = _.flow(add, square);
   * addSquare(1, 2);
   * // => 9
   */
  function flow() {
    var funcs = arguments,
        length = funcs.length;

    if (!length) {
      return function() {};
    }
    if (!arrayEvery(funcs, isFunction)) {
      throw new TypeError(FUNC_ERROR_TEXT);
    }
    return function() {
      var index = 0,
          result = funcs[index].apply(this, arguments);

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

  return flow;
});