Debug in NestJs Application With DI and dotenv

[360disrupt]

NestJs uses DI and dotenv for the configuration. I moved the initialization of the debug instance into the service constructor to make sure process.env.DEBUG is set. What confuses me is that this.debugSensorBoot.namespace === process.env.DEBUG is true but no log appears until it is manually enabled.

import debug from 'debug';
...
@Injectable()
export class SensorsService {
  debugSensorBoot: any;

  constructor() {
    console.log('process.env.DEBUG', process.env.DEBUG) // logs: process.env.DEBUG sensor:boot

    // (1) init debug
    this.debugSensorBoot = debug('sensor:boot');

    // (2) process.env.DEBUG is set - no logs appear
    console.log('this.debugSensorBoot', this.debugSensorBoot.namespace === process.env.DEBUG, this.debugSensorBoot.enabled) // logs: this.debugSensorBoot true false
    this.debugSensorBoot("Im not logging anything as I'm disabled") // does not log anything

    // (3) for example this works 
    this.debugSensorBoot.enabled = this.debugSensorBoot.namespace === process.env.DEBUG; // this is true as shown above
    this.debugSensorBoot("I log")
  }

I can add the .enable in the constructor as shown above but it seems quite hacky:

this.debugSensorBoot.enabled = this.debugSensorBoot.namespace === process.env.DEBUG; and it wouldn't work if it is equal.

[Qix-]

It's hard to tell without a repro case but are you initializing the environment before or after you include debug?

[360disrupt]

The import of debug happens before the config (.env) is loaded. And I think it's not possible to move that import statement into the constructor as it would be possible with require.

The initialization of the instance is afterward. In that moment the config is loaded and process.env.DEBUG exists.

I think passing an option like:

import debug from 'debug';
...
// later in the code e.g. constructor of a class
const debugInstance = debug('someInstance', {reloadEnv: true});

or

const debugInstance = debug('someInstance');
debug.reloadEnv();

Could solve that.

Or does this exist, when init or load is called? Actually I'm not quite understanding what is called when the instance is constructed/the module is imported.
https://github.com/visionmedia/debug/blob/6b07f9e50a528b6b47256d876f7e77374c337333/src/node.js#L209-L218

[Qix-]

The import of debug happens before the config (.env) is loaded.

I really don't believe this being the case. Without reproduction code, I can't assert either way.

Going to close for now. Let me know if this needs to be re-opened.