async in JavaScript

Author: mounishvatti

part2/async/intro.md

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+Blocking vs. Non-blocking 
+-------------------------
+
+In synchronous programming, the program will wait for a response from the
+operating system before continuing. This is known as blocking. In contrast,
+asynchronous programming allows the program to continue executing other
+operations while waiting for a response from the operating system. This is
+known as non-blocking.
+
+
+What is async?
+---------------
+
+Asynchronous programming is a style of programming in which operations are
+performed independently, in parallel, and asynchronously. This is in contrast
+to synchronous programming, where operations are performed one after the other,
+in sequence.
+
+In this section, we will look at how to write asynchronous code in JavaScript.
+
+
+What is an async function?
+--------------------------
+
+An async function is a function that returns a coroutine. A coroutine is a
+special type of object that can be used to suspend a function's execution and
+resume it later. When a coroutine is suspended, it can be resumed later, and
+when it is resumed, it picks up where it left off.
+
+The `async` keyword is used to declare a function as an async function. An
+async function can be called as a regular function, but it can also be called
+as a coroutine. When called as a coroutine, the function will return a
+coroutine object. The coroutine object can be used to suspend the function's
+execution and resume it later.
+
+Here is an example of an async function:
+
+```js
+async function foo() {
+  console.log('foo');
+}
+```
+
+When this function is called, it will return a coroutine object. The coroutine
+object can be used to suspend the function's execution and resume it later.
+
+```js
+const coro = foo();
+coro.next();
+```
+
+This will print `foo` to the console, and then suspend the function's
+execution.