Decorators

A decorator attaches extra behavior to a class or its members, written with an @ prefix — most commonly seen in frameworks like Angular and NestJS.

function logCalls(target: any, propertyKey: string, descriptor: PropertyDescriptor) {
    const original = descriptor.value;
    descriptor.value = function (...args: any[]) {
        console.log(`Calling ${propertyKey}`);
        return original.apply(this, args);
    };
}

class Calculator {
    @logCalls
    add(a: number, b: number) {
        return a + b;
    }
}

Decorators require "experimentalDecorators": true in older TypeScript configs (the syntax has since been standardized in JavaScript itself) — check which version your framework expects.