Logger decorator

#logger #methods #typescript #decorators

Typescript method decorator

Hey, often we make console.log(...) to see the value of a parameter or a result method.

Here I present you a decorator which allow to do it easily. It’s purpose is for debugging when you are developing something.

	interface LoggerParams {
	type?: 'log' \| 'trace' \| 'warn' \| 'info' \| 'debug';
	inputs?: boolean;
	outputs?: boolean;
	}

	const defaultParams: Required<LoggerParams> = {
	type: 'debug',
	inputs: true,
	outputs: true,
	};

	export function Log(params?: LoggerParams) {
	const options: Required<LoggerParams> = {
	type: params?.type \|\| defaultParams.type,
	inputs: params?.inputs === undefined ? defaultParams.inputs : params.inputs,
	outputs: params?.outputs === undefined ? defaultParams.outputs : params.outputs,
	};

	return function(target: any, propertyKey: string, descriptor: PropertyDescriptor) {
	const original = descriptor.value;

	descriptor.value = function(...args: any[]) {
	if (options.inputs) {
	console[options.type]('Logged inputs:', args);
	}

	const result = original.apply(this, args);

	if (options.outputs) {
	console[options.type]('Logged outputs', result);
	}

	return result;
	};
	};
	}

view raw log.decorator.ts hosted with ❤ by GitHub

Now that’s how to use it:

class Toto {
  @Log()
  public myMethod(...args: unknown[]): boolean { ... }

  @Log({ outputs: false })
  public myMethod2(...args: unknown[]): void { ... }

  @Log({ inputs: false })
  public myMethod3(...args: unknown[]): unknown { ... }

  @Log({ type: 'trace' })
  public myMethod4(...args: unknown[]): unknown { ... }

  @Log({ type: 'trace', inputs: false, outputs: false })
  public myMethod5(...args: unknown[]): unknown { ... }

}

Hope this could help or inspire someone.

Thanks for reading, feel free to comment.