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I am working with Elm. I have read about ports in Elm and how they can help in sharing data/messages between Elm and Javascript.

I am intending to work with a rich datetime library like moment.js. Suggest how to port moment.js or any other alternatives for this?

Yu Hao
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Gaurav Agarwal
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3 Answers3

16

There aren't any rich datetime libraries for Elm (AFAIK), so let's go with porting.

I took a quick look at this JavaScript library and it looks like most of its functionality doesn't rely on the current date/time, which I expect is the only side-effect used in a datetime library. So Elm ports are not going to be very helpful.

Solution 1 - translate the JS code to Elm code

This will obviously take some time, but should be fairly simple since it's mostly side-effect-free code.

Solution 2 - Native Elm library (No longer supported)

Update: Creating your own native modules is no longer supported starting with Elm 0.19.

Since most functions are pure, you might be best of writing a Native library. This way the functions from the moment.js can map one-to-one on functions in Elm.

Warning: Native libraries are generally discouraged.
The reason is that it's really an unsafe way to directly call JavaScript functions, no compiler checks, you can introduce arbitrary side effects, which would mess up the language. So it's not ideal. But if you make sure you only bind to pure functions from the JavaScript library, you can get away with it.
Have a look at an example native library, like elm-markdown to see how to write one. You will need the "native-modules": true indication in the elm-package.json file. If you want to publish the library on package.elm-lang.org it will need to be checked and approved first. You can ask for that on the mailing list.

Dull Bananas
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Apanatshka
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  • It's worth nothing that writing natives modules are highly discouraged by the founder of the language as it meant to be used only for kernel functionalities. See https://discourse.elm-lang.org/t/native-code-in-0-19/826 for more. – viam0Zah Jun 16 '20 at 11:12
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Don't rewrite the library in Elm. Elm plays nicely with the external world. Take a look at Elm Ports: https://guide.elm-lang.org/interop/ports.html

Newbyte
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Juanda
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4

In the mean-time, Elm 0.18 has gained a reasonable library for dealing with dates and times in elm-community/elm-time.

And Elm 0.19 comes with a new core time handling library: elm/time.

robx
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