Introduction
The Document Object Model (DOM) is a programming interface for HTML, XML, and SVG documents, which allows them to be access...
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I strongly disagree that Javascript interaction on the DOM is slow. Browsers handle DOM updates increadibly well and the DOM manipulation is even faster.
See this little example, that creates 10.000 bordered DIV´s containing some text. The content, background and layout will be updated for all elements in a loop and you can watch, how fast the changes are. Things are slowing down if you update 100.000 elements or more per second.
You can try out how many elements your machine is able handle by increasing the count.
The main argument that seem to have been misunderstood is that not updating the DOM (especially between render cycles) is faster than updating it, so frameworks try their best to avoid unnecessary updates.
However, in some cases, the amount of memory and CPU used for this task is worse for performance than updating the DOM, so one should take that argument with a grain of salt.
I did some research about the reasons, why pages are slow and unresponsive. You have to look at this in a very differentiated way; blanket statements like “Javascript is slow” are simply not helpful at all.
Compare to the time the DOM needs to be updated, there are many much slower things that are happening.
Each network request using the HTTP-protocol takes some fixed time the Round Trip Time that may 30 - 100 ms, but also longer under bad network conditions. Depending on your page structure you may load a module, evaluate it, load a depending module, evaluate it, start building a page, load some data from a database, evaluate it, fetch some depending data and so on...
You may get a chain of delays adding up to seconds.
Each module loaded will be executed once. If it performs some slow calculations or even if you just add a delay in your code, the application will need to wait until all modules are finished doing such operations. It is easy to write a html-page that takes many seconds before anything is displayed.
Finally it is true: Without Javascript you would not be able to have such a delay, but the reverse conclusion is simply not correct! You could also say: Without the internet websites would be much faster, as all delays are caused by the internet.