Posts Tagged ‘performance’

JavaScript includes and DOMContentLoaded event

Saturday, July 26th, 2008

My article about the non-blocking behavior of javascript includes was recently published on the YUI blog. Luke Chambers asked how does this method affect DOMContentLoaded event, so I gave it a shot.

The test examples are:

Basically, I added an event listener to document DOMContentLoaded event and to the onload events of every script, image and the document. I also exaggerated the loading time of scripts and images.

Results

Normal script tag

js: Sat Jul 26 2008 15:53:33 GMT-0700 (Pacific Daylight Time)
DOMContentLoaded: Sat Jul 26 2008 15:53:33 GMT-0700 (Pacific Daylight Time)
img2: Sat Jul 26 2008 15:53:37 GMT-0700 (Pacific Daylight Time)
img1: Sat Jul 26 2008 15:53:37 GMT-0700 (Pacific Daylight Time)
img6: Sat Jul 26 2008 15:53:37 GMT-0700 (Pacific Daylight Time)
img3: Sat Jul 26 2008 15:53:37 GMT-0700 (Pacific Daylight Time)
img5: Sat Jul 26 2008 15:53:37 GMT-0700 (Pacific Daylight Time)
img4: Sat Jul 26 2008 15:53:37 GMT-0700 (Pacific Daylight Time)
img8: Sat Jul 26 2008 15:53:40 GMT-0700 (Pacific Daylight Time)
img7: Sat Jul 26 2008 15:53:40 GMT-0700 (Pacific Daylight Time)
onload: Sat Jul 26 2008 15:53:40 GMT-0700 (Pacific Daylight Time)

DOM-included script

DOMContentLoaded: Sat Jul 26 2008 15:55:29 GMT-0700 (Pacific Daylight Time)
img1: Sat Jul 26 2008 15:55:32 GMT-0700 (Pacific Daylight Time)
img2: Sat Jul 26 2008 15:55:32 GMT-0700 (Pacific Daylight Time)
img6: Sat Jul 26 2008 15:55:32 GMT-0700 (Pacific Daylight Time)
img4: Sat Jul 26 2008 15:55:32 GMT-0700 (Pacific Daylight Time)
img3: Sat Jul 26 2008 15:55:32 GMT-0700 (Pacific Daylight Time)
img5: Sat Jul 26 2008 15:55:32 GMT-0700 (Pacific Daylight Time)
img8: Sat Jul 26 2008 15:55:35 GMT-0700 (Pacific Daylight Time)
img7: Sat Jul 26 2008 15:55:35 GMT-0700 (Pacific Daylight Time)
script: Sat Jul 26 2008 15:55:39 GMT-0700 (Pacific Daylight Time)
onload: Sat Jul 26 2008 15:55:39 GMT-0700 (Pacific Daylight Time)

In any event, the document onload waits for the script, no matter how it's included.

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Posted in experiments, performance | 1 Comment »