Javascript is a very fine language but contrary to Java there isn't any native documentation engine.
Some open source projects offer you ways to generate doc from javadoc like comment in your code :
  • JsDoc : It is a good perl generator for javascript doc but it impose upon user tgto follow a given way to write javascript because it tries to interpret some javascript instruction to generate documentation : 
                      /**
                   * Shape is an abstract base class. It is defined simply
                   * to have something to inherit from for geometric 
                   * subclasses
                   * @constructor
                   */
                   function Shape(color){
                     this.color = color;
                   }

                   // Bind the Shape_getColor method to the Shape class
                   Shape.prototype.getColor = Shape_getColor;
                    
                   /**
                    * Get the name of the color for this shape
                    * @returns A color string for this shape
                    */
                   function Shape_getColor(){
                     return this.color;
                   }
                    
                   /**
                    * Circle is a subclass of Shape
                    */
                   function Circle(radius){
                     this.radius = radius;
                   }
                    
                   /**
                    * A very rough value for pi
                    */
                   Circle.PI = 3.14;
                   
                   /**
                    * Get the radius of this circle 
                    * @returns The radius of this circle
                    */
                   function Circle_getRadius(){
                     return this.radius;
                   }
                  
                   // Circle is a subclass of Shape
                   Circle.prototype = new Shape(null);
  • JGrouse : It is much better when you want to use frameworks, because it allows documenting of Javascript classes, regardless which approach or framework is being used for it - be it Prototype, Dojo, Dean Edward's Base, jGrouse or any other. And it is fully integrated as ant Task :
    exemple using dojo
                      dojo.provide("net.demay.geometry.Shape");
                  /**
                   * Shape is an abstract base class. It is defined simply
                   * to have something to inherit from for geometric 
                   * subclassesl
                   * @class net.demay.geometry.Shape
                   * @author Vincent Demay
                   */
                  dojo.declare("net.demay.geometry.Shape", null, {

                   /**
                    * Color of the shape
                    * @variable {net.demay.color.Color} color
                   color : null,
                   
                   /**
                    * @constructor Shape
                    * @param {net.demay.color.Color} color
                    */
                   constructor: function(color){
                     this.color = color;
                   },
                    
                   /**
                    * Get the name of the color for this shape
                    * @function {net.demay.color.Color} return a color string for this shape
                    */
                   getColor: function(){
                     return this.color;
                   }
                 }



                  dojo.provide("net.demay.geometry.Circle");
                  /**
                   * A circle is a specific {@link net.demay.geometry.Shape
                   * @class net.demay.geometry.Circle
                   * @author Vincent Demay
                   * @extends net.demay.geometry.Shape
                   */
                  dojo.declare("net.demay.geometry.Circle", [net.demay.geometry.Shape], {            

                   /**
                    * Circle radius
                    * @variable {Float} radius
                    */
                   radius :  null,

                   //private no doc
                   PI : 3.14,

                   /**
                    * @constructor Circle
                    * @param {Float} radius
                    */
                   constructor: function(radius){
                     this.radius = radius;
                   },
                   
                   /**
                    * Get the radius of this circle 
                    * @function {Float} getRadius
                    */
                   getRadius : function(){
                     return this.radius;
                   }
                 }