up

8-async/05-promise-api/article.md

@@ -0,0 +1,53 @@
+# Promise API
+
+There are helpful static methods in the `Promise` class. There are only 4 of them, so we'll quickly cover them here.
+
+## Promise.all
+
+The method to run many promises in parallel and wait till all of them are ready.
+
+The syntax is:
+
+```js
+let promise = Promise.all(iterable);
+```
+
+It takes an `iterable` object with promises, for instance an array and returns a new promise that resolves with the array of their results when all of them are settled, or rejects with the first encountered error if any.
+
+For instance:
+
+```js run
+// loads 3 scripts in parallel and returns an array of them
+Promise.all([
+  loadScript('/article/promise-api/one.js'),
+  loadScript('/article/promise-api/two.js'),
+  loadScript('/article/promise-api/three.js')
+]).then(scripts => {
+  alert(`scripts loaded: ${scripts}`);
+});
+```
+
+
+
+- the returned `promise` awaits for al
+
+In the previous chapter we saw how to run things sequentially. Promises also
+
+- Promise.all
+- Promise.race
+- Promise.reject
+- Promise.resolve
+
+Let's meet more functions and methods for promises.
+
+
+
+Keywords `async` and `await` provide a more elegant way to write the code using promises.
+
+## Async functions
+
+The `async` function is like a regular one, but it wraps a returned value in a `Promise`.
+
+
+
+Nowadays, promises are de-facto standard for asynchronous actions, when we need to

8-async/05-promise-api/head.html

@@ -0,0 +1,13 @@
+<script>
+function loadScript(src) {
+  return new Promise(function(resolve, reject) {
+    let script = document.createElement('script');
+    script.src = src;
+
+    script.onload = () => resolve(script);
+    script.onerror = () => reject(new Error("Script load error: " + src));
+
+    document.head.append(script);
+  });
+}
+</script>

8-async/05-promise-api/one.js

@@ -0,0 +1,3 @@
+function one() {
+  alert(1);
+}

8-async/05-promise-api/three.js

@@ -0,0 +1,3 @@
+function three() {
+  alert(3);
+}

8-async/05-promise-api/two.js

@@ -0,0 +1,3 @@
+function two() {
+  alert(2);
+}