Surya JS Journey

Learn JavaScript through concepts, code, and guided practice.

A focused workspace for concept study, interactive examples, visual explanations, and challenge solving.

Concept Playground

Callbacks

Callbacks are a fundamental JavaScript pattern. They are used in array methods, event listeners, timers, and asynchronous APIs. Before promises and `async`/`await`, callbacks were the main way to handle async results, and they are still everywhere in the language today.

Mode

Practice mode

Run code, inspect output, and reset instantly.

Source

Loaded from a concept

Starter code is loaded directly into the editor.

File

callbacks.js

Same code, editable immediately in the browser.

Workspace Flow

1. Edit the snippet

Change the code freely to test ideas and edge cases.

2. Run and inspect

Use the output panel to confirm behavior and catch runtime errors.

3. Reset or continue

Restore the starter or branch into your own experiment.

Practice Workspace

callbacks.js

Edit the code, run it in the browser, and inspect the console output below. Reset restores the original snippet for this page.

Editor

8 lines

Output

0 entries

Mode

practice

Workspace Notes

Changes stay local until you run the code. Reset restores the original snippet immediately for another pass.

Live editing

Safe to change before every run.

Fast reset

Return to the original starter instantly.

callbacks.js

8 linesMonaco Editor

Editor Actions

Use the editor to explore the example, then run it to inspect the console.

Console0 entries

Run the code to see output here.

Expected Output

Starting lesson
Finished lesson

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