Instructions for using with wasm

[liquidscorpio]

While there are some issues/PRs (#243, #284, etc.) relating to wasm, there is no specific section in documentation properly detailing steps to use it with something like wasm-pack.

For now (v0.4.10), the following code fails to compile:

extern crate wasm_bindgen;

use wasm_bindgen::prelude::*;
use chrono::{NaiveDate};

#[wasm_bindgen]
pub struct Request {
    date: NaiveDate,
}

The error message is:

   | #[wasm_bindgen]
   | ^^^^^^^^^^^^^^^ the trait `wasm_bindgen::convert::FromWasmAbi` 
   | is not implemented for `chrono::naive::date::NaiveDate`

[quodlibetor]

Ah, yeah I actually have almost no experience with wasm other than getting the tests running. A PR adding wasm instructions (or pointing to them) would be most welcome!

[liquidscorpio]

If I do manage to get going, I will send in a PR documenting the same.
Still scratching my head for now in search of a work around related to the above issue. 😅

[quodlibetor]

You do need to build chrono with the wasmbind feature and (I believe) build using the wasm-pack tool, see the ci/travis.sh script, look for wasmbind.

[liquidscorpio]

This is the declaration I am using in the Cargo.toml file.

[dependencies.chrono]
version = "0.4"
default-features = false
features = ["wasmbind", "js-sys"]

On the other hand, the error message seems to be correct as an impl for wasm_bindgen::convert::FromWasmAbi is nowhere to be found in the code base. I'll dig further on how other datetime libs (outside of Rust) are handling this.

[da-x]

A way to get system time in wasm until both std's SystemTime and chrono are fixed, is the following, using stdweb:

std::time::Duration::from_millis(stdweb::web::Date::now() as u64)

[liquidscorpio]

@da-x That is one good way. My idea though was to leverage chrono's convenient date manipulation APIs.

[jonknapp]

In case it helps anyone else who stumbles here from the web like I did, I changed my wasm-pack built app's dependencies from:

[dependencies]
chrono = { version = "0.4", features = ["serde"] }

to

[dependencies.chrono]
version = "0.4"
features = ["serde", "wasmbind"]

and I'm able to serialize / deserialize DateTime<Utc> with:

use serde_derive::{Deserialize, Serialize};

#[derive(Deserialize, Serialize)]
stuct MyStruct {
    last_saved_at: DateTime<Utc>,
    other_field: usize,
}

Prior to adding the wasmbind feature, it would panic during runtime.

[pitdicker]

The wasmbind feature is enabled by default since #771.

So since then it should 'just work'?