Web - Timeline of a page load (Page Speed|Page Latency)

1 - About

Page load is the latency performance metrics that cumulates:

  • TCP latency (ie how fast, HTTP will be delivered)
  • and HTML latency (ie how fast a page will be rendered)

2 - Processing

HTML code is loaded by the browser in the order it appears in the file.

Load is not a single moment in time — it’s an experience that no one metric can fully capture. There are multiple moments during the load experience that can affect whether a user perceives it as “fast” or “slow”.

4 - Timeline

4.1 - Ready State Status

5 - Example

Webpack

6 - API

7 - Statistics

Your web analytics provider should provide you with them.

Example for Google Analytics

8 - Control

8.1 - Script

If JavaScript through the script element is placed before the body (without the HTML - Defer attribute attribute), it will therefore be loaded first and if it is supposed to affect the HTML in the body, it might not work, as the JavaScript would be loaded before the HTML it is supposed to work on.

Scripts in HTML have “run-to-completion” semantics, meaning that the browser will generally run the script uninterrupted before doing anything else (without the HTML - Defer attribute attribute), such as:

9 - Slow page

Probability of bounce by page latency.

(Slow pages lose user)

10 - User perception

  • 100 ms: user perceives as instantaneous
  • 1s: is about the upper limit of human flow of though. User loses the feeling direct feedback
  • 10s: Upper limit of attention. Feedback is important and the chance of context switch is high.

11 - Record

To record a page load, you would use a headless browser

12 - Utility

  • side-by-side-pageload.js - Load 2 or more pages side-by-side to visually see the difference in page load. Optional desktop viewport and throttling settings.

13 - Documentation / Reference


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