Koll NPM | npm.io

Koll

This is a very basic logging library mainly for communicating with grafana's faro backend.

It massively cuts back on functionality compared to opentelemetry + faro-web-sdk, and you should definitely just use those.
This is just the bare minimum that was enough for me.

Installation

npm install koll

Usage

To get started you need to set up an exporter, there is one included for communicating with faro, and a couple of utility exporters.

Here's an example:

import { lightBrowserDetect, measurement } from "koll"
import { faroExporter } from "koll/exporters/faro"
import { batchingExporter } from "koll/exporters/batching"

// the faroexporter attempts to mimic grafana faro's web-sdk.
const faro = faroExporter({
    // destination url where any messages will be sent
    destination: 'http://localhost:12345/collect',
    // the meta object describes the application sending the messages
    meta: () => ({
        // the 'app' is what will show up when looking for messages in loki / tempo
        app: {
            name: 'web',
            version: '0.0.1',
        },
        // you can also pass along routing information
        page: {
            url: location.href,
        },
        // you can add some browser info with this function, but if you really care
        // about browser stats you should use a real useragent parser.
        // or try to convince grafana to do it in the agent. :)
        browser: lightBrowserDetect()
    })
});

// it's a good idea to batch up the messages before sending them to a collector
// otherwise you get a whole lot of ongoing requests.
const batching = batchingExporter(faro, {
    // interval: 1000;         // how often to trigger sends
    // batchingInterval: 1000; // if a send is triggered, and there are more items left to send, this lets you use a shorter interval
    // maxBatchSize: 35;       // how many items to batch. you can max send 65kb per batch, otherwise sendbeacon will fail. so be careful.
    // maxQueueSize: 100000;   // if we get more messages than this in the queue we'll just start dropping old messages.
});

// an exporter is just a function that takes takes some items and processes them.
// you can add exporters to do things like add context to log items, set a sample rate, or anything really.
// it can be async or not.
const myExporter = async (...messages: ExportItem[]) => await batching(...messages);

When you have an exporter set up you're ready to send messages.

There are a few default instrumentations that can be enabled, these are just functions that will call the global exporter with logs and measurements. Let's look at those first:

import { instrumentResourceTiming } from "koll/instrument/resource-timing"
import { instrumentWebVitals } from "koll/instrument/web-vitals"
import { instrumentUnhandledErrors } from "koll/instrument/unhandled-errors"

// the resource timing instrumentation sends a timeline of resources that were loaded in from when the page started up until the window load event.
// this will give a nice timeline view in tempo.
instrumentResourceTiming(myExporter);

// web vitals is a cutdown version of the google web-vitals library reported as measurements to faro.
// it will track domload time, content layout shift, largest contentful paint and first contentful paint.
instrumentWebVitals(myExporter);

// the error instrumentation sends any errors to faro. it does the bare minimum needed to report errors correctly.
// if you call the return value the instrumenter will be shut down if needed. after shutting down instrumentErrors needs to be called again to re-enable it.
const stop = instrumentUnhandledErrors(myExporter, {
    // ignore: err => false   // you can pass in an ignore function to determine if an error should not be sent.
});

On top of that you can of course create your own traces and messages:

import {tracer} from "koll";

// the tracer function creates a Tracer object for carrying a parent context around.
// that can be helpful when you want to create nested traces.
const trace = tracer(myExporter, request.headers['traceparent']);

// run will execute an async function with a 'span' as an argument.
// that span will get timestamps based on when the function starts and stops.
// after completion it will send this data to the exporter.
const result = await trace.run('some-scope-name', async (span) => {
    // each span should at least have a name for context.
    span.name = 'getting some things';
    
    // you can also add attributes to it
    span.attributes.push({
        key: 'http.response_status',
        value: { intValue: 200 }
    });

    // or cancel it to prevent the span and any children of it from getting logged.
    span.cancel();

    // the span is also a Tracer object, so you can pass it around to let other functions
    // create logs or child spans referencing it.
    const result = await span.run('some-other-scope', (childSpan) => {
        // and finally there's a function to create a traceparent context that can be passed
        // along to other services.
        return await fetch('/', { headers: { traceparent: childSpan.traceparent() }});
    )});

    // whatever value you return will be returned from `trace.run`
    return result;
});

// you can also create measurements, which are just log messages.
trace.measurement('my-scope', 'http.response_time', 'ms', 200);

// and log messages. the second value is an opentelemetry severity.
//     0 = unspecified - do not use
//  1- 4 = trace
//  5- 8 = debug
//  9-12 = info
// 13-16 = warn
// 17-20 = error
// 21-24 = fatal
trace.log('my-scope', 20, 'error log message');

// there is also an exception function to log an error message.
trace.exception('my-scope', new Error('error message'));

// you can also create a span without the async function, which is useful if you
// want to describe events that have already happened and don't need to care about timing.
trace.span('my-scope', {
    name: 'my span',
    startTimeUnixNano: millitime(Date.now() - 10000),
    endTimeUnixNano: millitime(Date.now()),
});

Miscellaneous

There are a few little extras that can be useful.

web vitals

The web vitals instrumenter logs a few core web vitals, LCP, CLS, TTFB..

import { instrumentWebVitals } from "koll/instrument/web-vitals"

instrumentWebVitals(myExporter);

reporting navigation resource timing segments

The dom load performance instrumenter can be used for things like instrumenting loads during routing.

import {
    instrumentResourceTiming,
    reportResourceTimingSegment
} from "koll/instrument/resource-timing"

// you can instrument the entire documents loaded resources in one go
instrumentResourceTiming(myExporter);

// or report whatever segments you wants
const path = '/';
const start = performance.now();
await doRoutingStuff(path);
const end = performance.now();

reportResourceTimingSegment(`loaded ${path}`, start, end);

unhandled errors

The unhandled errors instrumentation does about what you'd expect.

It listens to error or promise rejection messages and logs them to an exporter.

import { instrumentUnhandledErrors } from "koll/instrument/unhandled-errors"

const stop = instrumentUnhandledErrors(myExporter, {
    // you can optionally ignore some errors
    ignore: err => false
});

// and if you get tired of logging the errors, you can stop!
stop();