TypeScript Decorators

LoggingDecorators.ts

function createSignature(instance, property, args) {
    var className = instance.constructor.name,
        argsString = args.map(JSON.stringify).join(', ');
    
    return `${className}.${property}(${argsString})`; 
}

export function LogMethodDecorator(): MethodDecorator {
    
    return function(target, property: string, descriptor: TypedPropertyDescriptor<Function>) {
        
        let method = descriptor.value;
        
        return {
            value: function(...args) {
                
                var out = method.apply(this, arguments);
                
                let signature = createSignature(target, property, args),
                    retValueString = JSON.stringify(out);

                console.log(`${signature} => ${retValueString}`)
        
                return out;
            }
        }
        
    }
    
}

ValidationDecorators.ts

function getValidators(target) {
    return this.__validators || (this.__validators = []);
}

export function ValidatableDecorator(): ClassDecorator {
    
    return function(target) {
        
        target.prototype.validate = function validate() {
            
            let validators = getValidators(this);
            
            for(let validator of validators) {
            
                let isValid = validator(this);
                
                if(!isValid) 
                    return false;
            }
            
            return true;
        }
        
    }
    
}

export function RequiredDecorator(): PropertyDecorator {
    
    return function(target, key) {
        
        let validators = getValidators(this);
        
        validators.push(function(instance) {
            var value = instance[key],
                isValid = (value || value === false); 
            
            if(!isValid) {
                console.log(`${key} is required`)
            }
             
            return isValid;
        });
    }
    
}