Detect runtime in code (js, dartvm, dartium)

[sethladd]

It would help to know which runtime the Dart program is running in. Options might be JavaScript, Dart VM in Dartium, Dart VM on command line.

[lrhn]

I'm wary at giving that information.
Currently the different platforms have different shortcomings, and I don't want users to write code that depends on, or codes around, these shortcomings based on the platform. Eventually the platforms should become mature enough that you shouldn't need to know the difference (at least between Dartium and dart2js, which should be indistinguishable).
I can see the need for detecting whether you are running in a browser or in the server VM, because that changes which libraries are available - but then, it might be more interesting to be able to check for the availability of a library.

[sethladd]

I think determining if you are running in a browser or server VM is sufficient. This is indeed about library availability.

[whesse]

But you currently can't use that knowledge at run time to conditionally include libraries, because libraries must be imported at compile time, not at run time. I think it is very important to maintain the property that all the source is known at compile time, rather than allowing code to included dynamically.

So we really need ways to write code for the browser and code for the standalone VM, and allow this code to share all of the common code and include the platform-specific code for the right platform, at deployment time.

A really simple base case for this problem would be to allow a cross-platform Timer, which would be implemented by Timer on dart:io and setTimeout on dart:html. There are good reasons why it is difficult to create the same timer interface on both platforms, but if someone wants a least-common-denominator shared class, to use in their code, they should be able to create one.

So, we need a way to change Dart code based on the configuration, but this need is at deployment time, not at run time. I think the package manager is supposed to help with this.

[sethladd]

Thanks Bill. We'd love to see a Timer interface that works where Dart works.

Perhaps John can elaborate on what his use cases are for this issue.

[sethladd]

This came up again: http://stackoverflow.com/questions/14655084/is-there-a-way-to-check-if-the-script-is-running-in-the-dart-vm-or-dart2js

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cc @kasperl.

[DartBot]

This comment was originally written by [email protected]

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As this method here now broke as well:

bool isDart() => js.scoped(() {
  try {
    // will throw exception if it doesn't exist
    var dartExists = js.context.navigator.webkitStartDart;
    return true;
  }
  on NoSuchMethodError {
    return false;
  }
});

I am really in favor of putting something stable into the API. Another reason for the need to know whether you're running in VM or not is spawnURI. If you run in a VM you can spawnURI a dart script, while when running in JS, you need to spawn a JS script..

[sethladd]

Try this:

identical(1, 1.0)

false in VM
true in dart2js

Obviously a hack, but it might work for you

[DartBot]

This comment was originally written by [email protected]

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Seth, I switched to that. But exploiting bugs is not a good way to determine whether something is running in dart2js or native on a VM.
It is like running "format c:" in a JVM to see if I am running on windows..

I think there are many interesting aspects that could be covered with a DartVM class that contains those information. For example:

• intPrecision
• doublePrecision
• dartVM version (in case you write 2.0 code but the vm is just 1.0)
• environmentType (isVM, isJS, isBrowser, isConsole)
• canSpawnDart
• canSpawnJavaScript

[DartBot]

This comment was originally written by [email protected]

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Similar: https://code.google.com/p/dart/issues/detail?id=11642

[lrhn]

There are no current plans to add information about the platform.
We should work to remove the differences, or make more specific information available (like canSpawnUri, not isVM). The former isn't future proof. If there end up being ten different implementations of Dart, we won't be able to expect the possible return values, and then we are back to user agent string parsing hell.
Feature detection, not platform detection.

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Added Library-Core, NotPlanned labels.

[DartBot]

This comment was originally written by [email protected]

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All proper languages that I am aware of have a mechanism to detect something about the environment in a clean way. Not including this in Dart is simply ignorant. The facts are:

• There will be different versions of Dart with different level of language support
• There might be different vendors
• There will be different platforms
• Not everyone can or wants to upgrade to the latest version
• Each version from every vendor contains bugs

While a good language combined with a good VM makes it almost unnecessary to detect what platform something is running on, like with Java, it sometimes is even on those platforms necessary to detect it. Be it to work around a specific bug in a specific version or to work around an issue about a certain platform.

[azenla]

I would like to propose that there be a simple environment flag (-Dx=y) set on each platform. Like this:

Dart VM (Server): -Dplatform=vm
Dart VM (Browser): -Dplatform=browser_vm
dart2js: -Dplatform=js

That would seriously make things easy.

bool get isServerVM => new String.fromEnvironment("platform") == "vm";
bool get isBrowserVM => new String.fromEnvironment("platform") == "browser_vm";
bool get isDart2JS => new String.fromEnvironment("platform") == "js";

The name 'platform' could be changed if needed.

[DartBot]

This comment was originally written by [email protected]

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Bluetooth on Linux is buggy. Right now, I need to disable bt support on Dartium Linux otherwise it crashes hard.

Specifically this bug here:

dart-gde/chrome.dart#215

Until such time Google can guarantee ALL FEATURES are always 100% stable on all platforms, users will need a way to look at even some basic platform information and gracefully degrade their app.

Otherwise, it just freaking crashes, and makes all other app development halt.

[DartBot]

This comment was originally written by [email protected]

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Also given that different chrome/dart versions may have bugs, being able to blacklist/degrade/workaround features/bugs on a given platform is absolutely needed to guarantee a good user experience.

[jtmcdole]

Note; path has a neat way of working around this.