validator.ts

import "reflect-metadata";

const REQUIRED_METADATA_KEY = Symbol("required");

function required(): ParameterDecorator {
	return function (
		target: Object,
		propertyKey: string | symbol,
		parameterIndex: number
	) {
		let existingRequiredParameters: number[] =
			Reflect.getOwnMetadata(REQUIRED_METADATA_KEY, target, propertyKey) || [];

		existingRequiredParameters.push(parameterIndex);

		Reflect.defineMetadata(
			REQUIRED_METADATA_KEY,
			existingRequiredParameters,
			target,
			propertyKey
		);
	}
}

function validate(): MethodDecorator {
	return function (
		target: Object,
		propertyName: string | symbol,
		descriptor: PropertyDescriptor
	) {
		let method = descriptor.value;
		descriptor.value = function () {
			let requiredParameters: number[] = Reflect.getOwnMetadata(
				REQUIRED_METADATA_KEY,
				target,
				propertyName
			);
			if (requiredParameters) {
				for (let parameterIndex of requiredParameters) {
					if (
						parameterIndex >= arguments.length ||
						arguments[parameterIndex] === undefined
					) {
						throw new Error("Missing required argument.");
					}
				}
			}

			return method.apply(this, arguments);
		};
	}
}

class Validator {
	@validate()
	caculate(
		@required() a?: any,
		@required() b?: any
	) {
		return a+b;
	}
}

console.log('result', new Validator().caculate())