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ChallengeIntermediate8 min

Predict the event loop output

Read mixed synchronous, promise, and timer code and determine the true execution order.

Without changing the code, explain which line logs first, second, third, and fourth. Then run it to verify your reasoning and write a short explanation of why promises resolve before the timeout callback.

Challenge Brief

Solve the exercise by editing the starter code and running it in the panel. Compare your result against the expected outcome, then refine your solution until the behavior matches.

  1. 1. Read the prompt carefully and identify the missing behavior.
  2. 2. Update only the parts of the starter code needed to solve it.
  3. 3. Run the code and compare actual output with the expected result.

Hints

  • Run through synchronous statements before looking at queued callbacks.
  • Promise callbacks go into the microtask queue.
  • Timers wait in the macrotask queue until microtasks are empty.

Related Concepts

Promise

Promises represent the eventual result of asynchronous operations and make async flows easier to compose.

Event Loop

The event loop coordinates synchronous code, queued tasks, and microtasks so JavaScript can handle async behavior.

Challenge Workspace

event-loop-order.js

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

Editor

11 lines

Output

0 entries

Mode

challenge

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.

event-loop-order.js
11 linesMonaco Editor
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Editor Actions

Run your solution and compare the result with the expected challenge output.

Console0 entries

Run the code to see output here.

Challenge Result

Run the code to check whether your solution matches the expected outcome.

Expected Output

A
D
C
B

Continue in Playground

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