Merge pull request #276 from odsantos/update--en-introduction-callbacks

Update "Introduction callbacks" English article

Author: odsantos

1-js/11-async/01-callbacks/article.md

@@ -43,7 +43,8 @@ If there's any code below `loadScript(…)`, it doesn't wait until the script lo
 
 ```js
 loadScript('/my/script.js');
-// the code below loadScript doesn't wait for the script loading to finish
+// the code below loadScript
+// doesn't wait for the script loading to finish
 // ...
 ```
 
@@ -59,7 +60,7 @@ newFunction(); // no such function!
 */!*
 ```
 
-Naturally, the browser probably didn't have time to load the script. So the immediate call to the new function fails. As of now, the `loadScript` function doesn't provide a way to track the load completion. The script loads and eventually runs, that's all. But we'd like to know when it happens, to use new functions and variables from that script.
+Naturally, the browser probably didn't have time to load the script. As of now, the `loadScript` function doesn't provide a way to track the load completion. The script loads and eventually runs, that's all. But we'd like to know when it happens, to use new functions and variables from that script.
 
 Let's add a `callback` function as a second argument to `loadScript` that should execute when the script loads:
 
@@ -76,6 +77,8 @@ function loadScript(src, *!*callback*/!*) {
 }
 ```
 
+The `onload` event is described in the article <info:onload-onerror#loading-a-script>, it basically executes a function after the script is loaded and executed.
+
 Now if we want to call new functions from the script, we should write that in the callback:
 
 ```js
@@ -101,7 +104,7 @@ function loadScript(src, callback) {
 *!*
 loadScript('https://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.2.0/lodash.js', script => {
   alert(`Cool, the script ${script.src} is loaded`);
-  alert( _ ); // function declared in the loaded script
+  alert( _ ); // _ is a function declared in the loaded script
 });
 */!*
 ```