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Gaëtan Redin
Gaëtan Redin

Posted on • Originally published at Medium on

2 2

Logger decorator

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;
};
};
}

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 { ... }

}
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Hope this could help or inspire someone.

Thanks for reading, feel free to comment.

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Top comments (1)

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nombrekeff profile image
Keff

Great stuff! I did something similar on an old angular project. But made it so it would only log stuff on development

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