7 ms·

Show HN: Percy – A Rust and WebAssembly isomorphic virtual DOM implementation

234 points by chinedufn 8y ago

jlebrech 8y ago
can you write an app in just once file and mark what can run in the client and what must only run on the server?
- chinedufn 8y ago
  As in an example app? If you don't need server side rendering you can have one Rust file but you also need a JS file to initialize the WebAssembly module. So just one file isn't reasonably possible. For a server side rendered app you need to have a cargo workspace with 3 crates (they can be in the same repo so not a huge deal). One crate is a `cdylib` that you compile to WebAssembly to serve your app to the client. This is a light wrapper around your actual application. One crate is your actual application. And one crate is your server, which is also a light wrapper around your actual application. That server side rendering structure can be found here - https://github.com/chinedufn/percy/tree/master/examples/isomorphic https://github.com/chinedufn/percy/tree/master/examples/isom... But in terms of a super minimal example without server side rendering.. I'll be working on adding one (along with updating the current example)!
  - jlebrech 8y ago
    what i want to see is to have all logic to be centered around features, and have a framework compile the server side and client server out of one logical piece of code, if that even makes sense. a bit like in the old days of php when you'd have the serverside code and html rendered in their, but this time nearly everything is running on the client unless the client can't be trusted. you could have some kind of ring system, where something can never run on the client right up to always run on client, but all in one file. but maybe that's nasty.
    - somenewacc 8y ago
      ASP.NET does this, you use its components and it generates client side javascript. In a more functional way, there's another language that does this caled Opa! http://opalang.org/ http://opalang.org/
      - jlebrech 8y ago
        yes, like runat="server" kinda thing.
- untog 8y ago
  React already does this, though perhaps not in the way you're imagining. You can use react-dom/server with your client side code to render out HTML templates, then when you run the code on the client side it'll call componentDidMount(), where you can add client-specific code.
nevi-me 8y ago
Hi chinedufn, this looks very interesting. I am at the same stage as you re. "I REALLY want to use this for everything ...". I see you're using wasm_bindgen quite a bit, but from a cursory look at the code; I can't figure out something: I can see how you're using wasm in the front-end, but could you please elaborate a bit more about in the backend? I presume that your backend is Rust based? I spent last weekend porting some code from NodeJS to a wasm module. I got it sort of working on Node, but haven't tried it on the browser yet (ran out of weekend). I'm quite optimistic about wasm [and Rust with wasm_bindgen]. I'd been thinking of writing a native add-on for Node, but the idea that I can use wasm instead is exciting.
- chinedufn 8y ago
  Sure! The backend is pretty much this (messy) file - https://github.com/chinedufn/percy/blob/master/examples/isomorphic/server/src/server.rs https://github.com/chinedufn/percy/blob/master/examples/isom... . It 1. Pulls in your application crate 2. Initializes your app (more or less sets initial state 3. Renders your app's virtual DOM into an HTML string 4. Serves the HTML to the client, along with the initial state serialized into JSON in a script tag (using serde-json) 5.Also serves the WASM script and the JS that initializes the WASM So that's your server crate. Then your client crate also pulls in your same application crate and you compile it to WebAssembly and that's what runs browser side. Feel free to let me know if any of that was poorly explained!
  - nevi-me 8y ago
    Thanks, that makes sense. I haven't built web servers with Rust as yet; so it was a bit difficult to follow the code.
    - steveklabnik 8y ago
      This is good enough for an example, but for a "real" web server, you wouldn't do this; you'd use a framework that handles a lot of this kind of thing for you. I think this code was adapted from the final chapter of the Rust book, which is mostly about learning how to write a simple thing than being production-ready.
dtx1 8y ago
Can someone ELI5(+) what an isomorphic virtual dom is?
- blattimwind 8y ago
  An isomorphic virtual DOM is much like an inverted-index homomorphic shadow DOM, but instead of using a shadowed mapping they virtualize the original elements themselves.
  - nicoburns 8y ago
    > An isomorphic virtual DOM is much like an inverted-index homomorphic shadow DOM, but instead of using a shadowed mapping they virtualize the original elements themselves. Not sure if this is ironic, but a 5 year old definitely wouldn't understand this!
    - tehlike 8y ago
      Given software/computers are part of curriculum now, i would not be surprised if we have some five year old already understanding this.
  - dtx1 8y ago
    I'm not sure if you are you are fucking with me or if i'm just ery stupid.... :(
    - navaati 8y ago
      AFAIK he's fucking with you ^^
      - chris_wot 8y ago
        Yup. Otherwise he's basically talking about a structure-preserving index that maps DOM elements - that are rendered outside the main document DOM tree - to a file. And that's not really what's going on here.
lovescalajs 8y ago
Another good tool if you want to write front end in a great general purpose language is scalajs. It allows you to reuse the dame Scala code for backend and front end.
thinkpad20 8y ago
How does this compare to the Yew framework?
- deleted 8y ago
  [deleted]
- chinedufn 8y ago
  Yew is awesome and just knowing that something like that was possible inspired Percy. I also looked at Yew's `html!` macro when figuring out how Percy's could / should work. One difference is that Yew is powered by stdweb and Percy is powered by wasm-bindgen. I'm personally SUPER bullish on wasm-bindgen because it's been designed from day 1 to be able to take advantage of the host bindings proposal when it materializes. Host bindings tl;dr is that instead of needing to go through JS to interact with browser APIs you can interact with them directly. Another difference is that to my knowledge Yew doesn't support server side rendering ( which was why I couldn't use it even though I wanted to :( ). Without having used Yew I don't want to comment any further than those high level differences. I can say that a big focus of Percy is to be a grab bag of modules / tooling for frontend Rust web apps with a major focus of you being able to swap out the parts that you think are bad for other peoples' better implementations. That dream isn't realized yet.. but I think that Rust's generics / traits could make this feel very clean!
  - JD557 8y ago
    >One difference is that Yew is powered by stdweb and Percy is powered by wasm-bindgen. >I'm personally SUPER bullish on wasm-bindgen because it's been designed from day 1 to be able to take advantage of the host bindings proposal when it materializes. I find it funny that you mentioned that. I actually was trying out wasm-bindget/yew recently and ended up using yew because of the wasm-bindgen limitations (mostly related to using anything with generics in the type signature). The experience will probably improve on the future, but right now yew's actor model seems like a much simpler way to encapsulate rust libraries.
andrethegiant 8y ago
Heads up, there's something already called Percy in the JS space. https://percy.io https://percy.io
- jhabdas 8y ago
  Pretty sure there's something called everything in the JS space. Thankfully this is the Rust/WASM space so all good names get to be recycled.
  - mekkkkkk 8y ago
    Damn, time to get started on React.rs. Is rQuery taken?
    - oconnor663 8y ago
      Not only is rQuery not taken, jQuery isn't taken either :-D
deleted 8y ago
[deleted]
jhabdas 8y ago
Has Facebook picked up on this yet? Good thing the Web is a Web of documents.
- steveklabnik 8y ago
  Facebook is a Rust user, but given that this was just announced, I doubt that they're suddenly using it ;) > Good thing the Web is a Web of documents. That was three for three years. It's been 23 years since we've had executable code as well.
- EugeneOZ 8y ago
  Good thing the Land is a land of dinosaurs.
_bxg1 8y ago
[makes side-eyes at React team to utilize webassembly]
- skybrian 8y ago
  Why? Has anyone shown this would be faster or a smaller download?
  - _bxg1 8y ago
    If they moved their virtual DOM (the meat of the work React does and its primary bottleneck) over to webassembly, it would almost certainly be faster. I can't really speak to the download size, though I wouldn't be surprised if that improved too.
    - julian37 8y ago
      It's worth keeping in mind that WebAssembly can't access the DOM directly; it has to call into JS in order to do that. I haven't investigated it myself but I'd wager that because of this, any performance benefits would be negligible. WebAssembly also can't access JS object structures directly, which means that the virtual DOM would have to live in WebAssembly land in the first place, ie. anything generated by JS that you want to end up in the DOM would have to be copied over first, or rather, you want all your VDOM-generating code to be WebAssembly code as well if you want the whole thing to be efficient.
      - _bxg1 8y ago
        The whole point of a virtual DOM is to simulate and reconcile changes before pushing those changes to the real DOM; it would be fairly clean to do all that processing in wasm and then send the result over to JS for reification. It's true that there would be some challenges when it comes to "sending" data to the virtual DOM; in particular, event objects could get complicated. I assumed this project has solved that problem, but I didn't read very deeply into it.
        8y ago
Buetol 8y ago
The use of the html macro is incredibly nice, no need for a special "JSX" language, it’s all builting thanks to macros. I’m working on the same thing for python (using pyxl/mixt/lys and brython) and you just proved that there’s interrest in that !

234 points by chinedufn 8y ago

jlebrech 8y ago

can you write an app in just once file and mark what can run in the client and what must only run on the server?

chinedufn 8y ago
As in an example app? If you don't need server side rendering you can have one Rust file but you also need a JS file to initialize the WebAssembly module. So just one file isn't reasonably possible. For a server side rendered app you need to have a cargo workspace with 3 crates (they can be in the same repo so not a huge deal). One crate is a `cdylib` that you compile to WebAssembly to serve your app to the client. This is a light wrapper around your actual application. One crate is your actual application. And one crate is your server, which is also a light wrapper around your actual application. That server side rendering structure can be found here - https://github.com/chinedufn/percy/tree/master/examples/isomorphic https://github.com/chinedufn/percy/tree/master/examples/isom... But in terms of a super minimal example without server side rendering.. I'll be working on adding one (along with updating the current example)!
- jlebrech 8y ago
  what i want to see is to have all logic to be centered around features, and have a framework compile the server side and client server out of one logical piece of code, if that even makes sense. a bit like in the old days of php when you'd have the serverside code and html rendered in their, but this time nearly everything is running on the client unless the client can't be trusted. you could have some kind of ring system, where something can never run on the client right up to always run on client, but all in one file. but maybe that's nasty.
  - somenewacc 8y ago
    ASP.NET does this, you use its components and it generates client side javascript. In a more functional way, there's another language that does this caled Opa! http://opalang.org/ http://opalang.org/
    - jlebrech 8y ago
      yes, like runat="server" kinda thing.
untog 8y ago
React already does this, though perhaps not in the way you're imagining. You can use react-dom/server with your client side code to render out HTML templates, then when you run the code on the client side it'll call componentDidMount(), where you can add client-specific code.

nevi-me 8y ago

Hi chinedufn, this looks very interesting. I am at the same stage as you re. "I REALLY want to use this for everything ...". I see you're using wasm_bindgen quite a bit, but from a cursory look at the code; I can't figure out something: I can see how you're using wasm in the front-end, but could you please elaborate a bit more about in the backend? I presume that your backend is Rust based? I spent last weekend porting some code from NodeJS to a wasm module. I got it sort of working on Node, but haven't tried it on the browser yet (ran out of weekend). I'm quite optimistic about wasm [and Rust with wasm_bindgen]. I'd been thinking of writing a native add-on for Node, but the idea that I can use wasm instead is exciting.

chinedufn 8y ago
Sure! The backend is pretty much this (messy) file - https://github.com/chinedufn/percy/blob/master/examples/isomorphic/server/src/server.rs https://github.com/chinedufn/percy/blob/master/examples/isom... . It 1. Pulls in your application crate 2. Initializes your app (more or less sets initial state 3. Renders your app's virtual DOM into an HTML string 4. Serves the HTML to the client, along with the initial state serialized into JSON in a script tag (using serde-json) 5.Also serves the WASM script and the JS that initializes the WASM So that's your server crate. Then your client crate also pulls in your same application crate and you compile it to WebAssembly and that's what runs browser side. Feel free to let me know if any of that was poorly explained!
- nevi-me 8y ago
  Thanks, that makes sense. I haven't built web servers with Rust as yet; so it was a bit difficult to follow the code.
  - steveklabnik 8y ago
    This is good enough for an example, but for a "real" web server, you wouldn't do this; you'd use a framework that handles a lot of this kind of thing for you. I think this code was adapted from the final chapter of the Rust book, which is mostly about learning how to write a simple thing than being production-ready.

dtx1 8y ago

Can someone ELI5(+) what an isomorphic virtual dom is?

blattimwind 8y ago
An isomorphic virtual DOM is much like an inverted-index homomorphic shadow DOM, but instead of using a shadowed mapping they virtualize the original elements themselves.
- nicoburns 8y ago
  > An isomorphic virtual DOM is much like an inverted-index homomorphic shadow DOM, but instead of using a shadowed mapping they virtualize the original elements themselves. Not sure if this is ironic, but a 5 year old definitely wouldn't understand this!
  - tehlike 8y ago
    Given software/computers are part of curriculum now, i would not be surprised if we have some five year old already understanding this.
- dtx1 8y ago
  I'm not sure if you are you are fucking with me or if i'm just ery stupid.... :(
  - navaati 8y ago
    AFAIK he's fucking with you ^^
    - chris_wot 8y ago
      Yup. Otherwise he's basically talking about a structure-preserving index that maps DOM elements - that are rendered outside the main document DOM tree - to a file. And that's not really what's going on here.

lovescalajs 8y ago

Another good tool if you want to write front end in a great general purpose language is scalajs. It allows you to reuse the dame Scala code for backend and front end.

thinkpad20 8y ago

How does this compare to the Yew framework?

deleted 8y ago
[deleted]
chinedufn 8y ago
Yew is awesome and just knowing that something like that was possible inspired Percy. I also looked at Yew's `html!` macro when figuring out how Percy's could / should work. One difference is that Yew is powered by stdweb and Percy is powered by wasm-bindgen. I'm personally SUPER bullish on wasm-bindgen because it's been designed from day 1 to be able to take advantage of the host bindings proposal when it materializes. Host bindings tl;dr is that instead of needing to go through JS to interact with browser APIs you can interact with them directly. Another difference is that to my knowledge Yew doesn't support server side rendering ( which was why I couldn't use it even though I wanted to :( ). Without having used Yew I don't want to comment any further than those high level differences. I can say that a big focus of Percy is to be a grab bag of modules / tooling for frontend Rust web apps with a major focus of you being able to swap out the parts that you think are bad for other peoples' better implementations. That dream isn't realized yet.. but I think that Rust's generics / traits could make this feel very clean!
- JD557 8y ago
  >One difference is that Yew is powered by stdweb and Percy is powered by wasm-bindgen. >I'm personally SUPER bullish on wasm-bindgen because it's been designed from day 1 to be able to take advantage of the host bindings proposal when it materializes. I find it funny that you mentioned that. I actually was trying out wasm-bindget/yew recently and ended up using yew because of the wasm-bindgen limitations (mostly related to using anything with generics in the type signature). The experience will probably improve on the future, but right now yew's actor model seems like a much simpler way to encapsulate rust libraries.

andrethegiant 8y ago

Heads up, there's something already called Percy in the JS space. https://percy.io https://percy.io

jhabdas 8y ago
Pretty sure there's something called everything in the JS space. Thankfully this is the Rust/WASM space so all good names get to be recycled.
- mekkkkkk 8y ago
  Damn, time to get started on React.rs. Is rQuery taken?
  - oconnor663 8y ago
    Not only is rQuery not taken, jQuery isn't taken either :-D

deleted 8y ago

[deleted]

jhabdas 8y ago

Has Facebook picked up on this yet? Good thing the Web is a Web of documents.

steveklabnik 8y ago
Facebook is a Rust user, but given that this was just announced, I doubt that they're suddenly using it ;) > Good thing the Web is a Web of documents. That was three for three years. It's been 23 years since we've had executable code as well.
EugeneOZ 8y ago
Good thing the Land is a land of dinosaurs.

_bxg1 8y ago

[makes side-eyes at React team to utilize webassembly]

skybrian 8y ago
Why? Has anyone shown this would be faster or a smaller download?
- _bxg1 8y ago
  If they moved their virtual DOM (the meat of the work React does and its primary bottleneck) over to webassembly, it would almost certainly be faster. I can't really speak to the download size, though I wouldn't be surprised if that improved too.
  - julian37 8y ago
    It's worth keeping in mind that WebAssembly can't access the DOM directly; it has to call into JS in order to do that. I haven't investigated it myself but I'd wager that because of this, any performance benefits would be negligible. WebAssembly also can't access JS object structures directly, which means that the virtual DOM would have to live in WebAssembly land in the first place, ie. anything generated by JS that you want to end up in the DOM would have to be copied over first, or rather, you want all your VDOM-generating code to be WebAssembly code as well if you want the whole thing to be efficient.
    - _bxg1 8y ago
      The whole point of a virtual DOM is to simulate and reconcile changes before pushing those changes to the real DOM; it would be fairly clean to do all that processing in wasm and then send the result over to JS for reification. It's true that there would be some challenges when it comes to "sending" data to the virtual DOM; in particular, event objects could get complicated. I assumed this project has solved that problem, but I didn't read very deeply into it.
      - 8y ago

Buetol 8y ago

The use of the html macro is incredibly nice, no need for a special "JSX" language, it’s all builting thanks to macros. I’m working on the same thing for python (using pyxl/mixt/lys and brython) and you just proved that there’s interrest in that !