The fetch API

View full source code or view the compiled example online

This example uses the fetch API to make an HTTP request to the GitHub API and then parses the resulting JSON.

Cargo.toml

The Cargo.toml enables a number of features related to the fetch API and types used: Headers, Request, etc.

[package]
name = "fetch"
version = "0.1.0"
authors = ["The wasm-bindgen Developers"]
edition = "2018"

[lib]
crate-type = ["cdylib"]

[dependencies]
wasm-bindgen = "0.2.83"
js-sys = "0.3.60"
wasm-bindgen-futures = "0.4.33"

[dependencies.web-sys]
version = "0.3.4"
features = [
  'Headers',
  'Request',
  'RequestInit',
  'RequestMode',
  'Response',
  'Window',
]

src/lib.rs

# #![allow(unused_variables)]
#fn main() {
use wasm_bindgen::prelude::*;
use wasm_bindgen::JsCast;
use wasm_bindgen_futures::JsFuture;
use web_sys::{Request, RequestInit, RequestMode, Response};

#[wasm_bindgen]
pub async fn run(repo: String) -> Result<JsValue, JsValue> {
    let mut opts = RequestInit::new();
    opts.method("GET");
    opts.mode(RequestMode::Cors);

    let url = format!("https://api.github.com/repos/{}/branches/master", repo);

    let request = Request::new_with_str_and_init(&url, &opts)?;

    request
        .headers()
        .set("Accept", "application/vnd.github.v3+json")?;

    let window = web_sys::window().unwrap();
    let resp_value = JsFuture::from(window.fetch_with_request(&request)).await?;

    // `resp_value` is a `Response` object.
    assert!(resp_value.is_instance_of::<Response>());
    let resp: Response = resp_value.dyn_into().unwrap();

    // Convert this other `Promise` into a rust `Future`.
    let json = JsFuture::from(resp.json()?).await?;

    // Send the JSON response back to JS.
    Ok(json)
}

#}