Log Decorator

log-decorator.ts

import { logClass } from './class-decorator';
import { logMethod } from './method-decorator';
import { logProperty } from './property-decorator';
import { logParameter } from './parameter-decorator';

// decorator factory - which calls the corresponding decorators based on arguments passed
export function log(...args) {
    switch (args.length) {
        case 3: // can be method or parameter decorator
            if (typeof args[2] === "number") { // if 3rd argument is number then its index so its parameter decorator
                return logParameter.apply(this, args);
            }
            return logMethod.apply(this, args);
        case 2: // property decorator
            return logProperty.apply(this, args);
        case 1: // class decorator
            return logClass.apply(this, args);
        default: // invalid size of arguments 
            throw new Error('Not a valid decorator');
    }
}

@log
class Employee {

    @log
    private name: string;

    constructor(name: string) {
        this.name = name;
    }

    @log
    greet(@log message: string): string {
        return `${this.name} says: ${message}`;
    }

}