Zone.js runs on tenfourfox but not firefox code#

In other words, if we’d like to run our code in a zone, we can already do it likes this: zone comes with a method run() that takes a function which should be executed in that zone. Once we’ve embedded zone.js into our website, we have access to the global zone object. Before we take a look at how we can profile our code samples with Zones, let’s first discuss how zones are created.

He created zone.js as a port of Zones to JavaScript, which is also a dependency of Angular. Brian (the guy I’ve mentioned earlier) has done exactly that. However, since Dart also just compiles to JavaScript, we can implement the same functionality in JavaScript too. Zones are actually a language feature in Dart. They can override methods within our code, or even associate data with individual zones. Zones can perform an operation - such as starting or stopping a timer, or saving a stack trace - each time that code enters or exits a zone. This is exactly where zones come into play. Sure, we could probably create and start an individual timer for each asynchronous operation manually, but that would get quite messy as asynchronous operations are added to the code sequence. So how do we solve this issue? What we need are basically hooks that allow us to execute some profiling code whenever such an asynchronous task happens. If this is entirely new to you, you might want to watch this great talk on how the browser event loops works. This is because asynchronous operations are added to the browser’s event queue, which eventually gets cleaned up by the event loop once there’s time for that. There is in fact one more operation, so it takes slightly longer to execute this code, however, the actual execution time of when the setTimeout() call returns is not part of the overall profiling. What effect does that have on our profiling? Well, we’ll see that there’s not such a big difference.

We extended the code sequence with another operation, but this time it’s asynchronous. Start = timer ( ) foo ( ) setTimeout (doSomething, 2000 ) bar ( ) baz ( ) // stop timer