TypeScript Class Decorator Generating metadata using a class decorator
Example
This time we are going to declare a class decorator that will add some metadata to a class when we applied to it:
function addMetadata(target: any) {
// Add some metadata
target.__customMetadata = {
someKey: "someValue"
};
// Return target
return target;
}
We can then apply the class decorator:
@addMetadata
class Person {
private _name: string;
public constructor(name: string) {
this._name = name;
}
public greet() {
return this._name;
}
}
function getMetadataFromClass(target: any) {
return target.__customMetadata;
}
console.log(getMetadataFromClass(Person));
The decorator is applied when the class is declared not when we create instances of the class. This means that the metadata is shared across all the instances of a class:
function getMetadataFromInstance(target: any) {
return target.constructor.__customMetadata;
}
let person1 = new Person("John");
let person2 = new Person("Lisa");
console.log(getMetadataFromInstance(person1));
console.log(getMetadataFromInstance(person2));
