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1. Revisit their usage periodically. Over time, it is likely the web page keeps downloading<br />
some JS that may no longer be needed, and removing it is the fastest and<br />
most effective resolution path!<br />
2. If the JS execution order is not critical and it must be run before the onload event<br />
triggers then set the “async” attribute, as in .<br />
This alone can improve your overall user experience tremendously, by downloading<br />
the JS in parallel to the html parsing. Watch out for document.write<br />
directives as they would most likely break your pages, so test carefully!<br />
3. If the JS execution ordering is important and you can afford to run the scripts<br />
after the DOM is loaded, then use the “defer” attribute, as in <br />
4. If the js is not critical to the initial view, then you should only fetch (and process)<br />
the js after the onload event fires.<br />
5. You can consider fetching the JS through an iframe if you don’t want to delay the<br />
main onload event, as it’ll be processed separately from the main page. However<br />
JS downloaded thru an iframe may not have access to the main page elements.<br />
If this sounds a tad complicated, it is because there is no one-size-fits-all to this problem,<br />
and it can be hazardous to recommend a particular strategy without knowing<br />
the business imperatives and the full html context. The list above though is a good<br />
starting point to ensure that no JS is left blocking the rendering of the page without a<br />
valid reason.<br />
Optimize images<br />
The relative and absolute weight of images for the most popular web sites keeps<br />
increasing over time. The Figure below is taken from httparchive.org and shows the<br />
number of requests and bytes size per page over the years.<br />
Best Practices for Web Performance | 19
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