utils.js

var path = require('path');

/**
 * Intercepts a method by replacing the prototype's implementation
 * with a wrapper that invokes the given interceptor instead.
 *
 *     utils.intercept(core.Element, 'inserBefore',
 *       function(_super, args, newChild, refChild) {
 *         console.log('insertBefore', newChild, refChild);
 *         return _super.apply(this, args);
 *       }
 *     );
 */
exports.intercept = function(clazz, method, interceptor) {
  var proto = clazz.prototype,
      _super = proto[method],
      unwrapArgs = interceptor.length > 2;

  proto[method] = function() {
    if (unwrapArgs) {
      var args = Array.prototype.slice.call(arguments);
      args.unshift(_super, arguments);
      return interceptor.apply(this, args);
    }
    else {
      return interceptor.call(this, _super, arguments);
    }
  };
};

exports.toFileUrl = function (fileName) {
  // Beyond just the `path.resolve`, this is mostly for the benefit of Windows,
  // where we need to convert '\' to '/' and add an extra '/' prefix before the
  // drive letter.
  var pathname = path.resolve(process.cwd(), fileName).replace(/\\/g, '/');
  if (pathname[0] !== '/') {
    pathname = '/' + pathname;
  }

  return 'file://' + pathname;
};

/**
 * Define a setter on an object
 *
 * This method replaces any existing setter but leaves getters in place.
 *
 * - `object` {Object} the object to define the setter on
 * - `property` {String} the name of the setter
 * - `setterFn` {Function} the setter
 */
exports.defineSetter = function defineSetter(object, property, setterFn) {
  var descriptor = Object.getOwnPropertyDescriptor(object, property) || {
    configurable: true,
    enumerable: true
  };

  descriptor.set = setterFn;

  Object.defineProperty(object, property, descriptor);
};

/**
 * Define a getter on an object
 *
 * This method replaces any existing getter but leaves setters in place.
 *
 * - `object` {Object} the object to define the getter on
 * - `property` {String} the name of the getter
 * - `getterFn` {Function} the getter
 */
exports.defineGetter = function defineGetter(object, property, getterFn) {
  var descriptor = Object.getOwnPropertyDescriptor(object, property) || {
    configurable: true,
    enumerable: true
  };

  descriptor.get = getterFn;

  Object.defineProperty(object, property, descriptor);
};

/**
 * Create an object with the given prototype
 *
 * Optionally augment the created object.
 *
 * - `prototyp` {Object} the created object's prototype
 * - `[properties]` {Object} properties to attach to the created object
 */
exports.createFrom = function createFrom(prototype, properties) {
  properties = properties || {};

  var descriptors = {};
  Object.getOwnPropertyNames(properties).forEach(function (name) {
    descriptors[name] = Object.getOwnPropertyDescriptor(properties, name);
  });

  return Object.create(prototype, descriptors);
};

/**
 * Create an inheritance relationship between two classes
 *
 * Optionally augment the inherited prototype.
 *
 * - `Superclass` {Function} the inherited class
 * - `Subclass` {Function} the inheriting class
 * - `[properties]` {Object} properties to attach to the inherited prototype
 */
exports.inheritFrom = function inheritFrom(Superclass, Subclass, properties) {
  properties = properties || {};

  Object.defineProperty(properties, 'constructor', {
    value: Subclass,
    writable: true,
    configurable: true
  });

  Subclass.prototype = exports.createFrom(Superclass.prototype, properties);
};