Add error to JsValue conversion and example (#691)

examples/wasm_github_fetch/src/lib.rs

@@ -0,0 +1,46 @@
+use serde::{Deserialize, Serialize};
+use wasm_bindgen::prelude::*;
+
+// NOTE: This test is a clone of https://github.com/rustwasm/wasm-bindgen/blob/master/examples/fetch/src/lib.rs
+// but uses Reqwest instead of the web_sys fetch api directly
+
+/// A struct to hold some data from the github Branch API.
+///
+/// Note how we don't have to define every member -- serde will ignore extra
+/// data when deserializing
+#[derive(Debug, Serialize, Deserialize)]
+pub struct Branch {
+    pub name: String,
+    pub commit: Commit,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct Commit {
+    pub sha: String,
+    pub commit: CommitDetails,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct CommitDetails {
+    pub author: Signature,
+    pub committer: Signature,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct Signature {
+    pub name: String,
+    pub email: String,
+}
+
+#[wasm_bindgen]
+pub async fn run() -> Result<JsValue, JsValue> {
+    let res = reqwest::Client::new()
+        .get("https://api.github.com/repos/rustwasm/wasm-bindgen/branches/master")
+        .send()
+        .await?;
+
+    let text = res.text().await?;
+    let branch_info: Branch = serde_json::from_str(&text).unwrap();
+
+    Ok(JsValue::from_serde(&branch_info).unwrap())
+}