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Use this script to detect slow users on your website, so you can improve their navigation.

Speed = User Experience

Slowness = Frustration

Think UX First. Remove non-important things from your interface when the user has already been waiting for ages.


  1. Include the uxfirst.min.js script in every page of your site. It simply saves the page load time in the user's localStorage. As it is tiny (less than 700 bytes before gzip), it is better if you inline it or concatenate with another script.

  2. Then, use this global function in your code: uxFirst(). It returns the average load time in milliseconds, for all the pages the user loaded on your site in the last 2 hours.

Before the first page is fully loaded, the average will be null (and null is the same as 0 when testing if it is > or < than a value).


	if (uxFirst() < 10000) {
		// Load ads for users having pages loading faster than 10 seconds


minNumberOfMeasures (optional)

The uxFirst function will return null as long as the number of measures is not reached. Default is 1.

// Wait for 3 measures before using uxFirst
if (uxFirst(3) < 10000) { ... }

It can help reducing yo-yo effect: the 1st page loads slowly - UXFirst helps accelerating the 2nd page and the average load-time gets under your limit - the 3rd page loads slowly again... The page content could look inconsistent if you use this script to remove a functionnality the user might be looking for.

Use cases

  • Don't load ads for users already having a slow navigation
  • Don't load some slow widgets
  • Use lower definition images or videos
  • Don't load custom fonts
  • Anything you can imagine to reduce user frustration

How slow is too slow?

Under 3 seconds, it is the ideal load time.

The average load time is near 7 seconds on the web.

Above 12 seconds, this is very slow and no-one should have to wait that long.


The script will work on E9+ and every other browser. When used on IE8 or IE7, the function uxFirst() will respond null, so you don't have to care about them not being supported.

This script uses the Navigation Timing API when it is available and has a fallback (less accurate) when it is not.


Feedback is very precious and any help is more than welcome!


Gaël Métais. I'm a webperf freelance. Follow me on Twitter @gaelmetais, I tweet mostly about Front-end and Web Performances.

I can also help your company about Web Performances, visit my website.


Small script that detects slow users so you can enhance their user experience




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