create addEventListener (#26486)

* create addEventListener

* Change title to lower case

* Rename file to index.md

Update and rename addeventlistener file to index.md. Also change front matter block to meet style guide

guide/english/javascript/add-event-listener/index.md

@@ -0,0 +1,59 @@
+---
+title: addEventListener
+---
+##addEventListener
+The addEventListener method assigns a function to a target event for a particular DOM element.  In simpler terms this method 
+says a function or block of code will be executed only when an event is triggered in the HTML DOM. This makes addEventListener 
+an important tool for making any webpage interactive.
+
+###Syntax
+```
+targetelement.addEventListener(event,callback function);
+
+where targetelement is the DOM element, event is the event to attach to the DOM element and callback function is the code 
+initiated when the event is triggered.
+```
+###Example
+```
+###HTML
+<div class=”container”>
+<div class=”row”>
+<button>First button</button>
+<button>Second button</button>
+<button id=”myButton”>Click My Button</button>
+<button>Fourth Button</button>
+</div>
+</div>
+
+###JavaScript
+document.getElementbyId(“myButton”).addEventListener(“click”,function(){
+                                                       alert(“This button has been clicked”);
+                                                        });
+```
+
+The previous line finds the HTML element with an id of “myButton” and attaches an event listener. In this case, the event is 
+“click” meaning whenever the use clicks on “myButton” “alert(’This button has been clicked’) “ will be executed. 
+
+###Note###
+addEventListener has several advantages . Firstly, it is possible to attach more than one event to a single element.  This adds 
+another layer of interactivity to your website. Second, it clearly separates the javascript code event handling from the HTML 
+structure. It is best practice that HTML, CSS and Javascript are kept modular. Lastly, it is possible to attach an event handler 
+to more than one element at once by using className or TagName. For example, the above code could be rewritten
+to apply to all the buttons.
+
+```
+document.getElementsByTagName (“button”).addEventListener(“click”,function(){
+                                                           alert(“This button has been clicked”);
+                                                           });
+
+
+```
+
+
+#### Other Resources
+<a href=https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener' target='_blank' rel='nofollow'>Mozilla Developer article on addEventListener</a>
+
+
+
+---
+