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Imagine a humongous web aplication built using Single Page Application framework such as AngularJS. With its each route it downloads a couple of HTML template files. Each of these template files contain JS files unique to it. So, now when each of these template files download it will also pull in and download the JS files as well.

This is just a hypothetical situation to understand how browsers would work under such a situation.

What will happen in terms of memory and performance when user quickly hops across all the pages (which can be 100s or 1000s of such pages)? Will all the JS variables consume the memory and unnecessarily clog it or will the JS Garbage Collector come to the rescue?

gnat
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Temp O'rary
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1 Answers1

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It depends upon your JavaScript code and your DOM (and in principle, of the JavaScript implementation in the browser; invite your users to use recent versions of browsers). You need to read more about garbage collection techniques (e.g. the GC handbook), see Mozilla SpiderMonkey's GC page.

A value which is still indirectly reachable from global or local variables won't be garbage collected. The GC will follow references in aggregate values (including closures, arrays, objects, ...).

You might want to carefully and cleverly use weak references, e.g. JavaScript WeakMaps.

Conceptually, the GC is computing the transitive closure of the reference graph, starting from global and local variables (on the call stack). These values are alive and the dead values are eventually destroyed by the GC since they are garbage. A value which is only reachable thru weak references won't be kept.

Even with a GC, a program can have a memory leak, in particular if it keeps in some variable a value which would never be useful in the future. And detecting this thru static code analysis techniques is an undecidable problem, provably equivalent to the halting problem.

Basile Starynkevitch
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  • Thanks. Apart from the javascript memory utilization. Can you tell me is there any limit on the number of JS files that can be downloaded by an application? AND if there are any browser based limitations set in Javascript memory utilizations and limit on the max size of the total number of JS/CSS files downloaded. – Temp O'rary Jan 15 '16 at 13:57
  • We live in a finite world, so there is some limit. I guess it is large enough that you should not care. You definitely need to benchmark and test your application. – Basile Starynkevitch Jan 15 '16 at 14:00
  • Yes. I am just trying to look at a worst of worst case and study what might happen in such cases. I'm trying to understand what would be the outcome in such situations. Since, I've never faced it. I've been always writting good code :) – Temp O'rary Jan 15 '16 at 14:08