introduce
What is bidirectional data binding?
Two-way data binding is aProgramming mode, used to implement data between the user interface and the data modelSynchronous updates. It allows data changes in the user interface to be automatically updated into the data model, and can also reflect changes in the data model to the user interface.
In bidirectional data binding, these changes are automatically updated to the data model when the user enters or modifies data on the interface. In turn, when the data in the data model changes, these changes will also be automatically reflected on the user interface, maintaining the data between the two.synchronous。
In this article, I will useBased on observer modeandBased on Proxy objectsTo implement custom two-way data binding of JS.
Methods for implementing observer mode
The observer pattern is a common design pattern that allows a one-to-many dependency between objects. In this mode, when an object's state changes, all objects that depend on it will be notified and automatically updated.
When implementing two-way data binding, we can create an observer object that is responsible for managing data changes and notifying relevant observers. We can useMethod to define a property and ingetandsetAdd the logic of the observer in the method. When the value of the attribute changes, the observer object will be notified and the corresponding update operation will be performed.
The advantage of this method is that it is easier to understand and implement. However, its disadvantage is that it requiresManualDefining the get and set methods for each property, this can become verbose and tedious for large applications.
Specific implementation method
// Define the observer classclass Observer {
constructor() {
= [];
}
// Add subscriber subscribe(callback) {
(callback);
}
// Unsubscribe unsubscribe(callback) {
= (subscriber => subscriber !== callback);
}
// Notify all subscribers notify(data) {
(subscriber => subscriber(data));
}
}
// Define a two-way binding classclass TwoWayBinding {
constructor() {
= '';
= new Observer();
}
// Set value setValue(value) {
= value;
(value);
}
// Get the value getValue() {
return ;
}
// Subscription value change event subscribe(callback) {
(callback);
}
// Unsubscribe to the value change event unsubscribe(callback) {
(callback);
}
}
// Create a two-way binding objectconst binding = new TwoWayBinding();
// Subscription value change event(value => {
('The value has changed:', value);
});
// Set value('Hello, World!');
// Get the valueconst value = ();
('Current value:', value);Let's take a closer look at the code example, and in the code we have defined aObserver classAsObserver, used to manage subscriber lists and notify subscribers. Then, we define aTwoWayBinding classAsTwo-way bindingImplementation, which contains a value and an observer object.TwoWayBinding classProvidedSet value、Get the value、Subscription value change eventandUnsubscribe to value change eventmethod.
You can implement custom two-way data binding by creating a TwoWayBinding object and then subscribing to the value change event. When the value changes, the subscriber will be notified and execute the corresponding callback function.
Implementation method of Proxy object
Proxy object is a new feature introduced in ES6, which can be used toIntercept and customize objectsoperation. By usingProxy Objects, we can add custom logic when accessing and modifying object properties.
When implementing two-way data binding, we can create a proxy object that intercepts access and modification operations to properties. When the value of the attribute changes, the proxy object will trigger the corresponding update operation, thereby achieving two-way data binding.
The advantage of this approach is that it is relatively concise and flexible. We do not need to manually define each propertygetandsetmethod, instead, it is automatically intercepted through proxy objects. However, its disadvantage is that it has poor compatibility and is not suitable for all browsers and environments.
Proxy implementation method
// Create an empty data objectconst data = {};
// Create a Proxy objectconst proxy = new Proxy(data, {
get(target, property) {
(`Read properties ${property}`);
return target[property];
},
set(target, property, value) {
(`Set properties ${property} for ${value}`);
target[property] = value;
// Here you can add logic to update the view return true;
}
});
// Access and modify data through Proxy objects = 'John'; // Set the property name to 'John'(); // Read properties name，Output 'John'In the above code, we create an empty data objectdata, then use the Proxy objectproxyProxy it. In Proxy objectgetandsetIn the method, we can customize the reading and assignment operations to attributes. In this example, we simply output information on the console to read and set the attribute and store the value of the attribute indatain object.
You can do as neededsetAdd logic to the method to update the view to achieve two-way data binding. When you modifyproxyWhen the object's properties,setThe method will be called. At this time, we can see the changes in the page UI in real time! !
Summarize
The implementation method based on Proxy object and the implementation method based on observer pattern are common software design patterns.
-
Implementation method based on Proxy object:
- A Proxy object is a proxy object that controls access to the underlying object and executes some extra logic before and after access.
- By using Proxy objects, you can enhance or modify the original object without modifying it.
- Proxy objects can be used to implement various functions, such as: caching, delayed loading, permission control, etc.
- When implementing a Proxy object, you usually need to define a handler that defines the logic to be executed when accessing a Proxy object.
-
Implementation method based on observer pattern:
- Observer pattern is a one-to-many dependency between objects. When an object's state changes, all its dependencies will be notified and automatically updated.
- The observer pattern consists of two main characters: Observers and Subject.
- The observer maintains an observer list and provides methods to register, log out and notify the observer.
- The observer defines the actions to be performed when a notification is received and can customize the observer's behavior as needed.
- The observer mode can be used to implement event processing, message delivery and other scenarios, providing a loosely coupled design method.
In summary, the implementation method based on Proxy object is mainly used to control and enhance the access of objects, while the implementation method based on observer pattern is used to implement notification and update mechanisms between objects.
The above is a detailed explanation of how to use JavaScript to implement customized two-way data binding. For more information about JavaScript two-way data binding, please follow my other related articles!