🔄
🧪 Simulate
LV2 · Toolooo Standard
Explore → See → Understand → ActUnderstand it. Feature Level describes the depth of the tool experience.

Browser Event Loop Simulator

Step through the call stack, microtasks, timers and rendering opportunities using safely parsed examples.

EngineeringFrontendJavaScriptPerformanceBrowser
🔒Your tool inputs are processed in your browser and are not uploaded or sent to analytics.
Supported subset and scheduler assumptions

Literal console.log; setTimeout with literal delay; Promise.resolve().then; queueMicrotask; requestAnimationFrame; top-level declared async functions with await Promise.resolve() and later zero-argument calls. Arrow callbacks use no arguments. Separate statements with semicolons. No variables, loops, intervals, network promises or arbitrary expressions.

The teaching scheduler drains microtasks after scripts/tasks and each rendering callback, orders timers by eligibility and insertion, and offers model frames every 16ms. Synchronous statements consume no modeled time. Real rendering and task-source ordering can differ. Source is parsed, never executed.

Prepare the example and step through it. Expected output: A → D → C → B.

Browser event-loop specification
What this tool does and why

Before you start

What

Step through the call stack, microtasks, timers and rendering opportunities using safely parsed examples.

Why

Microtasks wait for the running stack to unwind, while zero-delay timers only become eligible for a later task; seeing those queues explains surprising output order.

Your Result and Action update in the tool as you change its inputs.

Model note

This browser-side model explains the inputs you choose. Check an important decision against the real system, brief, or production constraints.

Next

Use the result to choose a connected next move.

Web Rendering Strategy Decision LabRank rendering patterns against freshness, personalization, hosting and discovery requirements.Client State & Storage Decision LabChoose browser state and storage mechanisms with transparent fit scores, capability constraints and privacy cautions.
How this tool stays honest

How it works

Parse a bounded JavaScript teaching subset without executing it. Follow synchronous logs, resolved Promise callbacks, microtasks, timer eligibility, async continuations and modeled rendering callbacks through a readable timeline with run, pause and step controls.

Assumptions

The tool runs in your browser and models the information you provide. It does not know facts outside that model.

Limitations

An educational parser models a limited syntax subset, not a JavaScript engine. It never executes source. Model frames occur every 16ms and timers use eligibility order; actual rendering, execution time and task sources differ. History is capped.

Understand Browser Event Loop Simulator

What this tool helps you understand

Parse a bounded JavaScript teaching subset without executing it. Follow synchronous logs, resolved Promise callbacks, microtasks, timer eligibility, async continuations and modeled rendering callbacks through a readable timeline with run, pause and step controls.

When to use it

When learning why asynchronous output appears in a particular order.

Try a scenario

Compare synchronous output, a promise microtask and a zero-delay timer. Inspect queue eligibility; the curated parser is not a full JavaScript runtime.

How to read the result

Read the active statement and stack before the queues. Compare microtask checkpoints with timer eligibility and modeled rendering opportunities; model timestamps are not performance measurements.

Assumptions and limits

An educational parser models a limited syntax subset, not a JavaScript engine. It never executes source. Model frames occur every 16ms and timers use eligibility order; actual rendering, execution time and task sources differ. History is capped.

Toolooo is part of Khizooology, created byKhizar Imtiaz (khizooo).