Does $(document).ready() Always Wait for CSS to Load?

Can $(document).ready() Trigger Before CSS is Loaded?

In the world of web development, timing is everything. For dynamic web pages, scripts often rely on CSS styles to be properly applied before they execute, affecting the presentation and functionality of elements on the page. The question arises: does the $(document).ready() event in jQuery guarantee that all CSS styles have been injected into the DOM before it triggers?

The official jQuery documentation suggests that you should include all CSS files before the scripts that use the $(document).ready() method. This ensures that all element properties are correctly defined before jQuery code executes.

However, experiments and analysis reveal that the behavior of $(document).ready() in relation to CSS loading can vary depending on browser and external resource dependencies. In some cases, browsers may delay JS execution until CSS is loaded, but in other instances, JS may execute concurrently with CSS downloads.

Despite inconsistencies in browser behavior, it's generally recommended to follow the jQuery documentation and place CSS before JS scripts to avoid potential problems. This ensures that when $(document).ready() executes, all CSS styles are available, preventing issues with misalignment or incorrect element sizing.

For those curious to delve deeper into the complexities of CSS and JavaScript loading, exploring resources like Steve Souders' "cuzillion.com" for script mimicking and webpagetest.org for waterfall analysis can provide valuable insights.

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