#You dont know js prototypal inheritance code

If youвЂ™re asking for help, include enough information for others to recreate your problem. With a nod to practicality, questions and posts about HTML, CSS, and web developer tools are also encouraged. Everyone should feel comfortable asking any and all JavaScript questions they have here. The apply() method enables you to modify the value of the this keyword when calling a function.This subreddit is a place for people to learn JavaScript together.

#You dont know js prototypal inheritance code

If you want to make the code in Listing 7 even shorter, then you can use the JavaScript apply() method. When the BaseControl() function is called, you want the keyword this to refer to the current object being built by the TreeViewControl constructor function.

The point of this code is to call the BaseControl constructor with the right value for the this keyword. You can use any property name here and the code would work the same way. It is important to understand that base is not a JavaScript keyword. Next, the base constructor function is called. The BaseControl function is assigned to a property of the TreeViewControl constructor function. Notice that the relationship between BaseControl and TreeViewControl is specified within the TreeViewControl constructor function with the following two lines of code: Of all of the methods of constructing objects described in this blog entry, I find this method the most intuitive and easy to use.

The TreeViewControl object inherits from the BaseControl object.ДЎ: 2: 3: function BaseControl() 4: 17: 18: // Create object 19: var treeView = new TreeViewControl() 20: 21: alert(treeView.PropA) // displays 'TreeViewControl PropA' 22: alert(treeView.PropB) // displays 'BaseControl PropB' 23: alert(treeView.PropZ) // displays undefined 24: 25: These classes represent visual controls (widgets) that might be used in a web page. Listing 1 contains two objects: BaseControl and TreeViewControl. This point is clearer with a sample of Prototype Inheritance in hand. Instead, you specify the prototype object with an objectвЂ™s constructor function. You donвЂ™t specify the prototype object for an object itself.

HereвЂ™s what is a little confusing about the way that Prototype Inheritance works. Therefore, when reading the value of PropA, the Prototype 2 object is ignored (lower objects in a chain can mask properties of higher objects in the chain). Prototype chains use a first match algorithm. In Figure 1, PropA is included twice: as a property of the original object and as a property of the Prototype 2 object. Notice that a prototype chain can contain duplicate properties. For example, if you attempt to read the value of PropC, the value of the property is retrieved from Prototype 1. When reading the value of a property from the object, the entire prototype chain is used to retrieve the value of the property. Prototype 2 has two properties named PropD and PropA. Finally, Prototype 1 also has a prototype object named Prototype 2. This objectвЂ™s first prototype object, Prototype 1, has one property named PropC. The object itself (located at the bottom of the figure) has two properties named PropA and PropB. In Figure 1, there is an object with two prototype objects in its prototype chain (a prototype chain is terminated with a Null value). Prototype Inheritance is illustrated by Figure 1. If the property is not found in the objectвЂ™s prototype chain, then the property value undefined is returned. Whenever you attempt to read a property, each link in the chain is checked for the property. Since the prototype object for an object can also have a prototype object, every object has something called a prototype chain. If you attempt to read a property from a JavaScript object, and the object does not have the property, then an attempt is made to read the property from the objectвЂ™s prototype. Every JavaScript object has an associated prototype object. Prototype Inheritance is the standard method of building JavaScript objects described in most JavaScript books and the Mozilla JavaScript documentation. At the very end of this entry, I briefly examine the approach taken by the ASP.NET AJAX framework. The goal of this blog entry is discuss the relative strengths and weaknesses of the two methods. For lack of better names, IвЂ™m calling the first method the Prototype Inheritance method and the second method the Xerox method. In this blog entry, I examine different methods of building new JavaScript objects from existing JavaScript objects.