add promise queue

1-js/11-async/07-async-await/01-rewrite-async/solution.md

@@ -0,0 +1,33 @@
+
+The notes are below the code:
+
+```js run
+async function loadJson(url) { // (1)
+  let response = await fetch(url); // (2)
+
+  if (response.status == 200) {
+    let json = await response.json(); // (3)
+    return json;
+  }
+
+  throw new Error(response.status);
+}
+
+loadJson('no-such-user.json')
+  .catch(alert); // Error: 404 (4)
+```
+
+Notes:
+
+1. The function `loadUrl` becomes `async`.
+2. All `.then` inside are replaced with `await`.
+3. We can `return response.json()` instead of awaiting for it, like this:
+
+    ```js
+    if (response.status == 200) {
+      return response.json(); // (3)
+    }
+    ```
+
+    Then the outer code would have to `await` for that promise to resolve. In our case it doesn't matter.
+4. The error thrown from `loadJson` is handled by `.catch`. We can't use `await loadJson(…)` there, because we're not in an `async` function.