Event Loop Utilization Observer

Get event loop utilization samples from a Node.js process (local or remote).

Integration

To add the observer to your application, use the ELUObserver class.

Example

const { ELUObserver } = require('event-loop-utilization-observer');

const observer = new ELUObserver((elu) => console.log(elu));

observer.observe({
    eluThreshold: 0.2,
    sampleIntervalMilliseconds: 20,
});

You can preload it as a seperate module with the -r flag in Node.js.

Attach to a running Node.js process

Use the RemoteELUObserver class to attach the observer to a running Node.js process.
This observer leverages the Chrome DevTools Protocol, and relies on the console.debug function for passing data.
So, if you see ELU logs in your application - take that into account and don't be alarmed.

Note

This observer depends on Node.js Inspector, so it might not be ideal for production.
If you need this observer in production anyway (for investigative purposes, for instance), you can tell Node.js to enable the inspector by running:

$ kill -SIGUSR1 <pid>

For more information refer to the Debugging Guide.

Example

const { RemoteELUObserver } = require('event-loop-utilization-observer');

(async () => {
    const obs = new RemoteELUObserver(
        (elu) => console.log(elu),
        { port: 9229 },
    );

    await obs.initialize();

    process.on('SIGINT', async () => {
        // be sure to disconnect the observer once you're done
        await obs.disconnect();
    });

    await obs.observe({
        eluThreshold: 0.2,
        sampleIntervalMilliseconds: 20,
    });
})();