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Table of Contents
What are the Performance Timeline and User Timing APIs?
How to use the User Timing API to mark critical time points?
What information can Performance Timeline record?
What should be paid attention to in practical applications?
Basically that's it
Home Web Front-end JS Tutorial Advanced JavaScript Performance Timeline and User Timing APIs

Advanced JavaScript Performance Timeline and User Timing APIs

Jul 19, 2025 am 03:57 AM

Performance Timeline and User Timing APIs are tools for precise measurement and analysis of web performance. Performance Timeline automatically records key events during the page loading process, such as navigationStart, domContentLoadedEventEnd and loadEventEnd; the User Timing API allows developers to manually mark time points through performance.mark(), measure time periods with performance.measure(), and finally get the result through getEntriesByType. In actual use, frequent calls and regular clean marks should be avoided, and performance data can be monitored efficiently with PerformanceObserver.

Advanced JavaScript Performance Timeline and User Timing APIs

JavaScript performance optimization is not only about reducing the amount of code or compressing resources, but more importantly, understanding the critical time points in the page loading and execution process. And Performance Timeline and User Timing APIs are the tools that help us do this. They allow us to measure and analyze page performance more carefully and find out where the bottleneck lies.

Advanced JavaScript Performance Timeline and User Timing APIs

What are the Performance Timeline and User Timing APIs?

Performance Timeline is a set of APIs provided by the browser, which are used to record various performance metrics during page loading and running, such as resource loading, repainting, parsing time, etc. The User Timing API is part of it, allowing developers to manually mark time points and measurement time periods, allowing for more flexibility in tracking the time-consuming of critical operations.

Both APIs are based on performance objects, and can obtain high-precision timestamps through performance.now() , with an error of less than one thousandth of a millisecond, which is more suitable for performance measurement than Date.now().

Advanced JavaScript Performance Timeline and User Timing APIs

How to use the User Timing API to mark critical time points?

The User Timing API provides several core methods:

  • performance.mark(name) : Creates a named timestamp mark.
  • performance.measure(name, startMark, endMark) : measures the time difference between two markers.
  • performance.getEntriesByType('measure') : Get records of all measurement types.

For example, if you want to measure how long it takes for a function to execute, you can do this:

Advanced JavaScript Performance Timeline and User Timing APIs
 performance.mark('start-processing');

// Some complex processing logic processData();

performance.mark('end-processing');
performance.measure('processing-time', 'start-processing', 'end-processing');

const measures = performance.getEntriesByType('measure');
console.log(measures); // The output is similar to { name: "processing-time", duration: 23.45, ... }

In this way, you can see the specific time-consuming on the console, which is convenient for subsequent optimization.


What information can Performance Timeline record?

In addition to manually marking time points, Performance Timeline also automatically records many performance events built into the browser. for example:

  • navigationStart : The point in time when the page starts loading.
  • domContentLoadedEventEnd : The time when DOM loading is completed.
  • loadEventEnd : The time when the entire page is loaded (including resources such as images).

You can view the timeline of all resources loading through performance.getEntriesByType('resource') , such as the time-consuming loading of images, scripts, stylesheets, etc.

This data can be used to analyze the loading performance of the first screen, find resources that are loading slowly, or determine whether certain non-critical resources should be delayed.


What should be paid attention to in practical applications?

Although these APIs are very powerful, there are some details to pay attention to when using them:

  • Don't call mark and measure frequently : Although they are not expensive in their own right, frequent logging will increase memory consumption, especially in long-running applications.
  • Clean up tags : Use performance.clearMarks() and performance.clearMeasures() to regularly clean up unnecessary tags to avoid data pileup.
  • In combination with PerformanceObserver : If you need to listen for certain types of performance entries (such as resource loading), you can use PerformanceObserver to listen for added entries instead of polling to get them.
 const observer = new PerformanceObserver((list) => {
  for (const entry of list.getEntries()) {
    console.log(entry.name, entry.duration);
  }
});
observer.observe({ type: 'measure', buffered: true });

This allows performance data to be processed more efficiently.


Basically that's it

Performance Timeline and User Timing APIs are not complex, but they provide a very practical performance analysis method. As long as you use it reasonably, it can help you understand the running status of the page more deeply and make more effective optimizations.

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