Runtime documentation for function declarations

doc.js

/**
 * Simple doc-property generator. Uses JavaDoc style comments.
 * Also provides type checking guards.
 *
 * Dependencies: SpiderMonkey >= 1.7
 *
 * by Dmitry Soshnikov <dmitry.soshnikov@gmail.com>
 * MIT Style License
 */

/**
 * include
 * @param {String} filename -- file to load and pre-process
 *
 * Loads source file and processes it with
 * forming __doc__ property of function declarations.
 * Also provides type checking guards. Finally, "eval"s
 * the source in the global context.
 *
 * TODO:
 *   - support FE (including anonymous)
 *   - better regexp to consider more cases
 */
function include(filename) {

  // get the source as a string
  var source = snarf(filename);

  var re = /(\/\*[^/]*\*\/)\s*(function\s*(\w*)\s*\([^)]+\)\s*{)?/;
  var globalRe = RegExp(re.source, "g");
  var singleRe = RegExp(re.source);

  source = source.replace(globalRe, function(data) {

    // separate doc-string, function name and header
    var [_, comment, header, name] = data.match(singleRe);

    // since function declarations are created on
    // entering the context, we may place __doc__ generation
    // before the function definiton itself (thus, we don't need to
    // find the closing } in the regexp, but only function header
    var transformedCode = name + ".__doc__ = " + '"' + comment.replace(/\n/g, "\\n") + '";';

    // validation code

    var paramsRe = /@param {(\w+)} (\w+)/g;
    var validationCode = [];
    var param;
    while (param = paramsRe.exec(comment)) {
      var paramType = param[1].toLowerCase();
      var paramName = param[2];
      // build simple validation if (typeof name != type) throw TypeError(...)
      validationCode.push(
        'if (typeof ' + paramName + ' != "' + paramType + '") ' +
        'throw TypeError(\'"' + paramName + '" must be a ' + paramType + '\');'
      );
    }

    return transformedCode + header + validationCode.join("");

  });

  ("global", eval)(source);

}

/**
 * help
 * @param {Function} fn
 * Prints help on a function
 */
function help(fn) {
  print('Help on "' + fn.name + '" function:\n');
  print(fn.__doc__);
}

source.js

/**
 * sum
 * @param {Number} x
 * @param {Number} y
 * The function of summation.
 */
function sum(x, y) {
  return x + y;
}

/**
 * multSum
 * @param {Number} x
 * @param {Number} y
 * @param {String} value
 * The function of calculation.
 */
function calculate(x, y, value) {
  // comment
  print(value + ": " + sum(x, y));
}

test.js

// load our library
load("doc.js");

// and the test source
include("source.js");

// ---------- Test documentation ----------

help(sum);

// Result:

// Help on "sum" function:
//
// /**
//  * sum
//  * @param {Number} x
//  * @param {Number} y
//  * The function of summation.
//  */

help(calculate);

// Result:

// Help on "calculate" function:
//
// /**
//  * multSum
//  * @param {Number} x
//  * @param {Number} y
//  * @param {String} value
//  * The function of calculation.
//  */

// ---------- Test guards ----------

sum(1, 2); // 3, OK

calculate(1, 2, "value"); // value: 3

sum(1, "2"); // TypeError: "y" must be a number

calculate(1, 2, 4); // TypeError: "value" must be a string