Bundle preloading in Firebase - Step-by-Step Execution

Process Flow - Bundle preloading

App starts loading

↓

Detect bundles needed

↓

Start preloading bundles

↓

Bundles download in background

↓

Bundles ready when needed

↓

App uses preloaded bundles

↓

Faster app startup and navigation

The app detects which code bundles it will need soon, starts downloading them early in the background, so when the user navigates, the bundles are ready and the app feels faster.

Execution Sample

Firebase

firebase.app().preloadBundles(['bundle1.js', 'bundle2.js']);
// Later when navigating
firebase.app().loadBundle('bundle1.js');

This code tells Firebase to start downloading bundles early, then later loads a bundle instantly from the preloaded cache.

Process Table

Step	Action	Bundle	Status	Effect
1	App starts	-	No bundles loaded	App begins loading
2	Detect bundles to preload	bundle1.js, bundle2.js	Scheduled	Bundles marked for preloading
3	Start preloading bundle1.js	bundle1.js	Downloading	Background download starts
4	Start preloading bundle2.js	bundle2.js	Downloading	Background download starts
5	bundle1.js download complete	bundle1.js	Ready	Bundle cached and ready
6	bundle2.js download complete	bundle2.js	Ready	Bundle cached and ready
7	User navigates to feature needing bundle1.js	bundle1.js	Loaded instantly	App uses preloaded bundle, fast load
8	User navigates to feature needing bundle2.js	bundle2.js	Loaded instantly	App uses preloaded bundle, fast load
9	No more bundles to preload	-	-	Preloading complete

💡 All bundles preloaded and used, app navigation is faster due to preloading

Status Tracker

Variable	Start	After Step 3	After Step 5	After Step 7	Final
bundle1.js status	Not loaded	Downloading	Ready	Loaded instantly	Loaded
bundle2.js status	Not loaded	Downloading	Ready	Loaded instantly	Loaded
preload queue	Empty	Empty	Empty	Empty	Empty

Key Moments - 3 Insights

Why does the app start downloading bundles before the user navigates to them?

Preloading bundles early means they are ready instantly when needed, avoiding waiting time during navigation (see execution_table steps 3-6).

What happens if the user never navigates to a preloaded bundle?

The bundle remains cached but unused, which is a trade-off for faster navigation if used (see execution_table step 9).

How does preloading improve app speed?

Because bundles are downloaded in the background before use, loading them later is instant (see execution_table steps 7-8).

Visual Quiz - 3 Questions

Look at the execution table, what is the status of bundle1.js after step 5?

A Loaded instantly

B Downloading

C Ready

D Not loaded

💡 Hint

Check the 'Status' column for bundle1.js at step 5 in the execution_table

At which step does the app use the preloaded bundle1.js?

A Step 7

B Step 3

C Step 5

D Step 9

💡 Hint

Look for 'Loaded instantly' status for bundle1.js in the execution_table

If bundle2.js never finishes downloading, what would happen when the user navigates to it?

A It loads instantly from cache

B App waits for download to complete

C App crashes

D Bundle is ignored

💡 Hint

Consider the meaning of 'Ready' and 'Downloading' statuses in the execution_table

Concept Snapshot

Bundle Preloading in Firebase:
- Detect bundles needed soon
- Start downloading bundles in background
- Cache bundles when ready
- Load bundles instantly on navigation
- Improves app speed and user experience

Full Transcript

Bundle preloading means the app starts downloading code bundles early, before the user needs them. This way, when the user navigates to a feature, the bundle is already downloaded and loads instantly. The process starts with detecting which bundles will be needed, then downloading them quietly in the background. Once downloaded, bundles are cached and ready. When the user navigates, the app uses the cached bundles, making the app feel faster. If a bundle is never used, it remains cached but unused. This trade-off helps improve app speed and smoothness.