Introduction

Flare can collect and display structured log messages from your JavaScript application, separate from error reports. This gives you insight into what your application is doing, beyond just the errors it throws.

Logs are buffered in the browser and shipped to Flare in batches as their own entity. They show up in your project's logs view, independent of any error report.

Logging is available in @flareapp/js (version 2.3.0 and up). The React, Vue and Svelte packages re-export the same client, so the API described here works there too.

Enabling log collection

Log collection is disabled by default — no log traffic is sent until you switch it on. Enable it with the enableLogs option, after calling flare.light():

import { flare } from '@flareapp/js';

flare.light('YOUR PROJECT KEY');

flare.configure({
    enableLogs: true,
});

While enableLogs is false, every flare.logger.* call is a no-op. Turning it back off again clears any buffered logs that haven't been shipped yet.

Recording logs

Once enabled, record a log through flare.logger. There is a method for each severity level:

flare.logger.info('User signed in');
flare.logger.warning('Slow response from the API');
flare.logger.error('Checkout failed');

Each method takes a message and an optional attributes object with structured data for that single log entry:

flare.logger.info('User signed in', { userId: 42, plan: 'pro' });

The full set of methods is debug, info, notice, warning, error, critical, alert, and emergency. See Levels for what each one means and how to filter them.

How logs are shipped

Logs are not sent one by one. The client buffers them and flushes a batch to Flare when any of these happens:

• the buffer reaches maxLogBufferSize records (default 100),
• the buffered payload reaches logFlushMaxBytes (default ~800 KB),
• the logFlushIntervalMs timer fires (default 5000 ms after the first buffered log), or
• the browser tab is hidden (visibilitychange → hidden), e.g. on navigation or closing the tab.

The unload flush uses fetch with keepalive so the request survives the page going away. Browsers cap keepalive request bodies, so on that path the client ships the most recent records that fit within keepaliveMaxBytes (default ~60 KB) and drops older overflow.

A log can only be shipped once a project key is set. If you record logs before flare.light() runs, they stay buffered and are sent on the next flush after the key is available.

Flushing manually

flare.flush() forces the buffered logs to be sent immediately. This matters when the page is about to do something that bypasses the normal unload flush, or in environments where the tab-hidden trigger doesn't fire:

await flare.flush();

Configuration options

Logging behaviour is tuned through flare.configure():

These options live alongside the error-reporting options on the installation page.

Disabling log collection

Set enableLogs back to false to stop collecting. Any logs still in the buffer are discarded:

flare.configure({ enableLogs: false });