JavaScript Benchmark Builder
Compare the performance of two JavaScript snippets online. Paste code A and code B, run each of them repeatedly for a chosen duration, and see the operations per second (ops/s) plus which version is faster and by how much.
FreeOnline Tool
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How to Use
- Paste the two JavaScript snippets you want to compare into the "Code A" and "Code B" boxes
- Set the duration of each run (500 ms by default); longer runs give steadier numbers but take longer to finish
- Click "Start" and the tool repeatedly executes each snippet until the duration is reached, counting the iterations and computing operations per second (ops/s)
- When the run finishes, both results are shown side by side together with a verdict telling you which snippet is faster and by what percentage
- Click "Load sample data" to see a ready-made comparison between map and Array.from for converting an array
Features
- Duration-based benchmarking: instead of a fixed iteration count, each snippet runs as many times as it can within the chosen number of milliseconds, avoiding skewed results from a badly chosen loop count
- Uses performance.now() for high-resolution timing, calculates operations per second and formats large numbers with K/M units
- Automatically compares the two results and labels which one is faster along with the exact percentage difference
- Parse errors and runtime exceptions in your code are caught and reported with a clear message instead of freezing the page
- Code runs locally in your own browser sandbox and is never uploaded to a server
Use Cases
Comparing array and object idioms
Measure common alternatives such as map vs forEach, a for loop vs forEach, or spread syntax vs Object.assign before committing to one.
Verifying that an optimization actually helped
Benchmark the code before and after a refactor to confirm with real timing data that the change made things faster.
Backing up technical decisions with data
Bring measured numbers instead of opinions to a design discussion or code review when arguing that one approach performs better.
Learning how the JavaScript engine behaves
Test different syntax and API choices yourself to build intuition about how engine optimizations affect real execution speed.
FAQ
Do I get the same numbers every time I run the benchmark?
Not exactly. Results are affected by the current load on your machine, the state of the browser's JIT optimizations and background processes, so some variation is normal. Run the test a few times and judge the overall trend rather than a single absolute number.
What duration should I use for each run?
The default 500 ms works for most cases. If the two snippets perform very similarly, increase the duration (1000-3000 ms) for a steadier, more reliable comparison, at the cost of waiting longer for the result.
What happens if my code throws an error?
If a snippet fails to parse or throws at runtime, the tool catches the error and shows the specific message. The page will not freeze or crash.
Where does the code run, and is that safe?
Snippets are executed through the browser's native Function constructor inside the page's own JavaScript runtime, so everything stays in your local browser sandbox and nothing is uploaded. Even so, never paste code from a source you do not trust.