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npm and iojs with new es6 features #269
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how about a
v8engine option?@JonathonOng: Yeah, I discussed that in paragraph 4, but it does have user experience issues. Do you have thoughts on those? That also won't provide a solution to other kinds of iojs incompatibility that may not be coming this month, but could happen.
I think that there is potential for io.js to introduce new apis not directly tied to V8 that may also lead to this situation. Ultimately, all new features introduces by io.js not available under node would likely require a
feature-xxxdeclaration on the package. Correct me if I'm wrong, but I think generally npm ecosystems could help solve this problem in a simple way (e.g. limit search to "packages that leverage ES7await"). In the end, it would be first, up to developer to decide whether to give that package a try and, secondly, to feature detect and polyfill when necessary. The same is true for node right now with packages like native-or-promise or async-listener for example.There is some overlapse with the
enginesdefinition, but with time, versions will have less meaning, just like user agents, and become a bigger burden to developers to maintain.I'm -1 on using engines for this.
Best practice is for module authors to feature detect when possible, this would encourage them not to do that.
There actually should be a "cost" to using new features prior to them being widely adopted but I wouldn't rule out the possibility of people creating tooling for older versions of node that check for modules using new features and compile them down to ES5.
Agreed. Several packages targeted at node 0.11 (especially for generators stuff) are recommending users to rely on transpilers such as
regeneratorfor node 0.10 compatibility. And then there's always Traceur and 6to5 runtimes for those who want to ES6 features in node and do not want make the switch to io.js just yet.v8engine option makes the most sense imho.I agree that testing v8 versions doesn't really give you any more information since there now will be combinations of what flags io.js (or node.js) is started with.
@mikeal how about exposing those features through package.json somehow? That at least give package to package feature dependencies over doing it within the modules (I can see scenarios where it wouldn't make sense to test for certain features since you'd probably wouldn't even install it in the first place without the feature in place). These entries could probably even be generated.
It is possible to automatically find out version of V8 (and any other parameters that affect compatibility) from specified engine and version, and use it, when later there will be another version compatible with specified.
For example, if specified
{ "engines": { "iojs": ">=1.0.0" } }and node 0.15+ will be compatible with iojs 1.0, when you will try to install on old node version, error message will say that you neediojs >= 1.0.0ORnode >= 0.15, which is compatible.And when you will install this package on
node >= 0.15it will just warn, that current engine is not same, that was specified, but is compatible.@sunflowerdeath npm could certainly keep a table of iojs and node versions and their associated v8 versions, and so translate iojs >= 1.0.0 into v8 >= x.x.x. I don't think we currently can see other parameters that effect compatibility though. But yeah, io.js could expose those, but for that to work node.js would also have to be convinced to expose them.
I'd love to see both - a consistent "engines" notation, which indicates what it's been /tested/ on, and a parallel "features" notation (I do not care about the name, bikeshed all you want), which indicates which JS features it depends on. Then it's left up to the npm cli, or the transpiler, or the saas platform, or whatever (or some npm module) to determine dynamically what is required to make the module work, or whether it's possible at all. Thoughts?
Currently, all my packages that use generators have a
foo.es6.jswith the actual source, afoo.es5.jswith transpiled code that is generated by theprepublishscript, and afoo.jsthat feature-detects and requires the appropriate file.
No need for magic inpackage.json, and works across all engines. It might be nice to have a more convenient wrapper around this kind of feature detection / transpilation.I'm not thinking "magic" as much as "documentation" - your approach is great, but how am I to know that's the format you've used? As described, I'd have to duck type it, whereas with a
package.jsonnotation, you'd explicitly call out what you supported.adding more metadata to package.json about language features used, or v8 versions tested against/supported:
- complicates package.json
- easily causes package.json to become out of date
- easily causes package.json to contain incorrect information
These are all fine, so long as you are vigilant about updating your package.json, but if we're honest, most people aren't.
automating detection of features used:
- makes assumptions about how you're going to use the module (transpiling? different version of node/iojs? loading a particular build shipped with the module?)
- causes headaches when using or developing modules
This seems like a really, really bad thing to bake into npm, and probably not a very good thing to do in an individual project either (although it's obviously up to you to make the call on how you ship your project)
Currently, all my packages that use generators have a
foo.es6.jswith the actual source, afoo.es5.jswith transpiled code that is generated by theprepublish script, and afoo.jsthat feature-detects and requires the appropriate file.Yes, oh 1000 times yes. That being said it wouldn't be bad practice (although not required) for something in package.json for batch scripts doing analytics. Not everything can be polyfilled via a transpiler. For those things I wouldn't want
npmto warn me, but it's also a like riding a Ferrari to the grocery store to need static analysis to figure this out from a machine perspective.👍 for using
package.json mainpoint to compiled ES5 source. 🍻 🐴11 remaining items
Example feature-detection package: has-generators
// foo.js module.exports = require('has-generators') ? require('./foo.es6') : require('./foo.es5')
If your stuff requires multiple ES6 things,
(require('has-foo') && require('has-bar')) ? … : ….
We can create these tiny little packages with ease for all the ES6 features that are available in io.js today.I actually have https://www.npmjs.com/package/make-generator-function published for an implicit "has-generators" check :-)
Why is this a problem?
Let people specify old versions of modules if they don't want to update node. They can already do this without any changes or feature detection stuff.
Let's not create a python2/python3 situation here.
Embrace progress. Don't create Frankensteins.
Anything distributed that's not in commonJS format is a python2/python3 situation. In order to support ES6 module syntax, anything we come up with will have to piggyback on top of an included CJS module as the default export, and every version (old and new) will have to work in old nodes too ¯_(ツ)_/¯
FWIW, I do feature detection at installation time. It has the benefit of not needlessly bloating your runtime with feature detection libraries. I suppose the detection library could do both, but this solved my immediate needs.
IMO this is more a messaging issue.
As has already been discussed, version detection is unreliable. Feature detection is better, but could easily explode in complexity as more and more new features are added and used.
On http://iojs.org/es6.html we explicitly state the language support differences. I think people that use these features in modules should be explicitly stating the requirements to use those modules. Obviously there's the possibility of people not bothering with it, but the same can be said of the engines field.
I do like the idea of using some magic thing to convert es6 code to work with es5 though.
Doesn't seem like there's really much we can do here. Re-open if this (es6 + node/io.js + npm) needs to be discussed more.
Just for anyone looking to build cross-compatible packages, here's one of mine as a reference:
FWIW, I do feature detection at installation time. It has the benefit of not needlessly bloating your runtime with feature detection libraries. I suppose the detection library could do both, but this solved my immediate needs.
What if I
npm installyour package while I'm using io.js, but later I use n to switch to Node 0.10 for some reason? (As a dev working on several projects I switch around all the time). Then your package would just fail to work, and it wouldn't necessarily be obvious why. Feature detection at runtime seems like a safer option.@callumlocke it could also be argued that you shouldn't have development environments depend on global set up and tooling, but rather have project local configuration – I tend to use Vagrant for things like that. Either way this is going off topic, and so I won't delve too deep into it. If you'd like to discuss feel free to tweet me or something.
For what it's worth, we've been more or less accomplishing the aim with https://github.com/bevry/esnextguardian
Since io.js is going to be getting a new v8, and thus a slew of new es6 features not previously enabled by default, this is going to create a situation where some modules will only work with io.js, at least, until such time as node.js updates its own v8.
The feature in npm that currently handles this kind of thing is package.json engines field.
Now there’s an obvious problem if we add an “iojs” engine type: future versions of node will be likely be api & v8 compatible with iojs, and so depending on a specific iojs version would incorrectly block those node versions.
If adding an “iojs” engine type is out, another option would be to add a “v8” engine type. This would solve the immediate problem, but end users don’t ordinarily think or care about v8 versions, and telling them “your v8 is too old” would be a very crappy user experience (and wouldn’t give them any immediate information on how to fix the problem).
So a third option would be to create a series of “feature-xxx”* modules (eg feature-generators) that have preinstall scripts that fail with meaningful messages if you try to install them in an environment without the feature. These wouldn’t import functionality, obviously, they’d just assert a engine that can handle the feature. Further, if one desired to, even in-development features could easily be supported with major version bumps as their implementation changes.
* Perhaps not actually "feature-xxx", another prefix would do just as well, maybe even just "v8-xxx"?
What do you all think? Do you have other ideas on how we might handle this?