1. Definition
The template method is based on an inherited design pattern, which can greatly improve the scalability of the system. Abstract parent class and child class in java
The template method consists of two parts of structure. The first part is the abstract parent class and the second part is the concrete implementation subclass.
2. Example
Coffee or Tea
(1) Boil water
(2) Soak the tea leaves in boiling water
(3) Pour the tea into the cup
(4) Add lemon
/* Abstract parent class: drink */
var Beverage = function(){};
// (1) Boil water = function() {
("Bring the water to boil");
};
// (2) Soak in boiling water = function() {
throw new Error("Subclasses must override brew method");
};
// (3) Pour into the cup = function() {
throw new Error("Subclasses must override pourInCup method");
};
// (4) Add seasoning = function() {
throw new Error("Subclasses must override the addCondiments method");
};
/* Template method */
= function() {
();
();
();
();
}
/* Implement subclass Coffee*/
var Coffee = function(){};
= new Beverage();
// Rewrite non-public methods = function() {
("Brew coffee with boiling water");
};
= function() {
("Populate coffee into a cup");
};
= function() {
("Add milk");
};
var coffee = new Coffee();
();
Through the template method pattern, the algorithm framework of the subclass is encapsulated in the parent class. These algorithmic frameworks are suitable for most subclasses under normal conditions, but "personality" subclasses will also appear.
As mentioned above, adding seasoning is optional.
The hook method can solve this problem, and placing hooks is a common way to isolate changes.
/* Add hook method */
= function() {
return true;
};
= function() {
();
();
();
if(()) {
();
}
}
/* Implement subclass Tea*/
var Tea = function(){};
= new Beverage();
// Rewrite non-public methods = function() {
("Brew tea with boiling water");
};
= function() {
("Populate the tea into the cup");
};
= function() {
("Add milk");
};
= function() {
return ("Do you need to add seasoning?");
};
var tea = new Tea();
();
JavaScript does not provide true class inheritance, which is implemented through delegates between objects.
3. "Hollywood Principles": Don't call us, we will call you
Typical usage scenarios:
(1) Template method mode:Using this design pattern means that the subclass gives up control over itself and instead notifies the subclass to the parent class. As a subclass, it is only responsible for providing some design details.
(2) Observer mode:Publishers push messages to subscribers.
(3) Callback function:ajax asynchronous request encapsulates the operations to be executed in the callback function. This callback function is executed only after the data is returned.
I hope that the description in this article will be helpful to everyone to learn JavaScript programming.