How to Log Events in Firebase Analytics: Simple Guide

To log an event in Firebase Analytics, use the logEvent method on the Firebase Analytics instance, specifying the event name and optional parameters as key-value pairs. This records user actions for analysis in the Firebase console.

Syntax

The logEvent method requires two parts: the event name as a string, and an optional object with parameters describing the event details.

• eventName: A string identifying the event, like purchase or login.
• params: An optional object with key-value pairs giving extra info, such as item_id or value.

javascript

firebase.analytics().logEvent(eventName, params);

Example

This example shows how to log a purchase event with details about the item bought and its price.

javascript

import { initializeApp } from 'firebase/app';
import { getAnalytics, logEvent } from 'firebase/analytics';

const firebaseConfig = {
  apiKey: "YOUR_API_KEY",
  authDomain: "YOUR_AUTH_DOMAIN",
  projectId: "YOUR_PROJECT_ID",
  storageBucket: "YOUR_STORAGE_BUCKET",
  messagingSenderId: "YOUR_SENDER_ID",
  appId: "YOUR_APP_ID",
  measurementId: "YOUR_MEASUREMENT_ID"
};

const app = initializeApp(firebaseConfig);
const analytics = getAnalytics(app);

logEvent(analytics, 'purchase', {
  item_id: 'sku1234',
  item_name: 'T-shirt',
  value: 19.99,
  currency: 'USD'
});

Output

Event 'purchase' logged with parameters {item_id: 'sku1234', item_name: 'T-shirt', value: 19.99, currency: 'USD'}

Common Pitfalls

Common mistakes when logging events include:

• Using event names or parameter keys that are too long or contain invalid characters. Event names must be under 40 characters and use only letters, numbers, and underscores.
• Not initializing Firebase Analytics before calling logEvent.
• Passing parameters in the wrong format, such as non-string keys or unsupported value types.
• Logging too many events or parameters, which can exceed Firebase limits.

javascript

/* Wrong: event name with spaces and special chars */
logEvent(analytics, 'purchase item', {value: 20});

/* Right: valid event name and parameters */
logEvent(analytics, 'purchase_item', {value: 20});

Quick Reference

Item	Description	Example
Event Name	String identifier for the event, max 40 chars, letters/numbers/underscores only	purchase_item
Parameters	Optional object with key-value pairs describing event details	{item_id: 'sku1234', value: 19.99}
Initialization	Firebase app and analytics must be initialized before logging events	const analytics = getAnalytics(app);
Limits	Max 500 different event types and 25 parameters per event	Avoid excessive custom events

Key Takeaways

Always initialize Firebase Analytics before logging events using logEvent.

Use valid event names with letters, numbers, and underscores only, max 40 characters.

Pass parameters as an object with simple key-value pairs for extra event details.

Avoid logging too many events or parameters to stay within Firebase limits.

Check Firebase console to verify events are recorded correctly.