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For a quick timing of a synchronous function, record performance.now() before and after the call and subtract the timestamps. In Node.js, you can also use node:perf_hooks to observe function calls. A measured duration describes that run, input and environment—not a universal speed ranking.
Time a synchronous function in a browser
The global performance.now() method returns a high-resolution timestamp in milliseconds on a monotonic time base. Subtracting the start timestamp from the later one gives elapsed time:
const start = performance.now();
const result = calculate(input);
const elapsedMs = performance.now() - start;
console.log({ elapsedMs, result });Keep logging outside the timed interval when measuring a small function: console output may take longer than the operation and distort the result. The timer has finite precision, and browser privacy or security protections may reduce it.
Use marks and measures for a larger operation
When you want to time a meaningful application task, give its start and end named marks, then create a measure between them. This makes the duration available as a named performance entry that can be used with browser performance tooling.
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- Valued Carpenter Pencil Set: You will get 2 pcs solid carpenter pencils with 26 piece 2.8 mm refills, 1 replaceable sharpener, 1 plastic storage box.The complete carpenter pencils combination allows you to finish your work faster and more easily
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performance.mark("calculate-start");
const result = calculate(input);
performance.mark("calculate-end");
performance.measure("calculate", "calculate-start", "calculate-end");
const entry = performance.getEntriesByName("calculate", "measure").at(-1);
console.log(entry.duration, result);For long-running instrumentation, clear marks and measures after collecting them so unnecessary timeline entries are not retained. A PerformanceObserver can collect new entries as they arrive. See MDN’s User Timing guide.
Measure function calls in Node.js
Node.js provides the stable node:perf_hooks module, which includes Web Performance API features and Node-specific measurements. Its timerify() wrapper records function timing entries; subscribe to the function entry type to receive them.
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import { performance, PerformanceObserver, timerify } from "node:perf_hooks";
const observed = timerify(calculate);
const observer = new PerformanceObserver((list) => {
for (const entry of list.getEntries()) {
console.log(`${entry.name}: ${entry.duration} ms`);
}
observer.disconnect();
});
observer.observe({ entryTypes: ["function"] });
observed(input);For a promise-returning function, Node reports its timing after the promise settles. Check the documentation for the Node.js version you deploy in case its API differs.
Measure asynchronous work through completion
If the question is how long an asynchronous operation takes overall, include the wait until it completes—not just the time needed to return a promise. In a browser, place the ending mark at the actual completion point. In Node.js, timerify() reports promise-returning function timing once the promise settles.
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Rank #3
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Compare implementations fairly
A single timed call is not enough to establish that one implementation is generally faster. Make the workload repeatable and hold relevant conditions steady:
- Choose representative input and verify that both implementations produce equivalent results.
- Repeat the operation. Allow runtime optimization and other environmental effects to settle before collecting observations for comparison.
- Use the same runtime and version, machine, input, and measurement method for each candidate.
- Report an appropriate summary or distribution, along with enough setup detail for someone else to reproduce the comparison. There is no single sample count or warm-up duration that suits every workload.
- If the concern is application speed, profile the broader workload too. A function microbenchmark does not establish end-to-end user experience.
Node’s documentation also describes histogram and benchmark-comparison facilities. Its core repository has dedicated benchmark tooling for runtime implementations and JavaScript code.
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Rank #4
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What can affect the result?
- Timer precision:
performance.now()is not infinitely precise. Browser security and privacy measures may coarsen its resolution. MDN documents its timestamp and behavior, while its high-precision timing overview compares it withDate.now(). - Clock choice:
Date.now()measures wall-clock time and has integer-millisecond resolution.performance.now()is monotonic and is generally the better choice for short elapsed-time measurements. Browsers may differ in whether it advances during operating-system sleep or browser process freezing; this matters more for long timings than tiny synchronous calls. - Runtime and workload: JavaScript engines, runtime versions, input, machine conditions and competing activity can change results. State which setup you measured rather than declaring a universal winner.
- Instrumentation: Keep unrelated work, such as logging, outside a small timed interval. Measure the operation that matters without adding avoidable overhead to the code being timed.
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