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8-async/03-promise-chaining/article.md

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+# Promises chaining
+
+There are many great things about promises. We're only starting.
+
+Now we'll cover promises chaining. They allow to build sequences of asynchronous actions.
+
+[cut]
+
+Here's the idea:
+
+```js run
+new Promise(function(resolve, reject) {
+  // do a job...
+  setTimeout(() => resolve(1), 1000);
+}).then(function(result) {
+
+  alert(result); // 1
+  return result * 2;
+
+}).then(function(result) {
+
+  alert(result); // 2
+  return result * 2;
+
+}).then(function(result) {
+
+  alert(result); // 4
+  return result * 2;
+
+});
+// ...
+```
+
+As you can see:
+
+- Calls to `.then` can be chained -- that's because `promise.then` returns a promise.
+- A value returned by `.then` becomes a result in the next `.then`.
+
+If there's an error, it is also passed down the chain:
+
+
+```js run
+new Promise(function(resolve, reject) {
+  setTimeout(() => resolve(1), 1000);
+}).then(function(result) {
+
+  throw new Error("Woops!");
+
+}).catch(function(error) {
+
+  alert(error.message); // Woops!
+
+});
+```
+
+
+
+
+The idea is :
+
+- A callback in `.then` may return a result.
+
+
+One of main purposes of promises is to make asyn
+The main purpose of promises
+Promises
+
+Promises can be chained. That allows actions to follow one after another.
+
+Here's a simple example first:
+
+```js
+let promise = new Promise(function(resolve, reject) {
+  setTimeout(() => resolve(""))
+})
+
+
+
+What if we want to
+The main idea behind promises
+Promises can be used for asynchronous tasks that eventually finish with a result or an error.
+
+We already have `loadScript`