Performance

`performance.now`

Returns a high-resolution timestamp in milliseconds representing the time elapsed since the page started loading

Syntax

JavaScript

performance.now()

Return Value

A DOMHighResTimeStamp (floating-point number of milliseconds)

Examples

Basic Usage

const start = performance.now()
// ... some operation
const end = performance.now()
console.log(`Took ${end - start}ms`)

Practical Example

function measure<T>(fn: () => T): [T, number] {
  const start = performance.now()
  const result = fn()
  const duration = performance.now() - start
  return [result, duration]
}

Advanced Usage

async function benchmark(fn: () => Promise<void>, iterations = 100) {
  const times: number[] = []
  for (let i = 0; i < iterations; i++) {
    const start = performance.now()
    await fn()
    times.push(performance.now() - start)
  }
  const avg = times.reduce((a, b) => a + b, 0) / times.length
  console.log(`Avg: ${avg.toFixed(2)}ms`)
}

Understanding performance.now

The performance.now method in JavaScript returns a high-resolution timestamp in milliseconds representing the time elapsed since the page started loading. It belongs to the Performance object and is one of the most widely used methods for working with performance values in modern JavaScript and TypeScript applications.

The method signature is performance.now(). When called, it returns a domhighrestimestamp (floating-point number of milliseconds). Understanding when and how to use now() helps you write more expressive, readable code.

Common use cases for performance.now include data transformation, input validation, API response processing, and building reusable utility functions. It works well alongside related methods like performance-mark, performance-measure, enabling you to chain operations together for complex data manipulation pipelines.

Browser support for performance.now is excellent across all modern browsers including Chrome, Firefox, Safari, and Edge. It is also fully supported in Node.js and Deno. For older environments, transpilation with Babel or a polyfill may be needed.