CODESAMPLE
Extension Object - TypeScript
The Extension Object pattern allows adding new functionality to an existing object without modifying its core code. This is achieved by creating a separate “extension” object that holds the new methods, and then composing the original object with the extension. This promotes the Open/Closed Principle – open for extension, closed for modification.
The TypeScript implementation uses object composition. The extend function takes the base object and one or more extension objects, returning a new object that inherits properties from all inputs. This is idiomatic TypeScript as it leverages the language’s flexible object model and avoids inheritance-based modification. The use of object literals and the spread operator (...) for composition are standard TypeScript practices for creating new objects with combined properties.
// Base object
const baseObject = {
name: "Base",
describe(): string {
return `This is ${this.name}`;
},
};
// Extension object 1
const extension1 = {
version: "1.0",
getDetails(): string {
return `Version: ${this.version}`;
},
};
// Extension object 2
const extension2 = {
author: "John Doe",
authorDetails(): string {
return `Author: ${this.author}`;
},
};
// Function to extend the object
function extend(base: any, ...extensions: any[]): any {
return Object.assign({}, base, ...extensions);
}
// Extend the base object
const extendedObject = extend(baseObject, extension1, extension2);
// Use the extended object
console.log(extendedObject.describe()); // Output: This is Base
console.log(extendedObject.getDetails()); // Output: Version: 1.0
console.log(extendedObject.authorDetails()); // Output: Author: John Doe
console.log(extendedObject); // Output: { name: 'Base', describe: [Function: describe], version: '1.0', getDetails: [Function: getDetails], author: 'John Doe', authorDetails: [Function: authorDetails] }