Supercharging our example website

Now we‘ve gone over a few JavaScript basics, let‘s add a few cool basic features to our example site to give you some first idea of what is possible.

Adding an image changer

In this section we‘ll add another image to our site, and add some simple JavaScript to change between the two when the image is clicked on.

1. First of all, find another image that you‘d like to feature on your site. Make sure it is the same size as your first image, or as close as possible.
2. Save the image in your images folder.
3. Go to your main.js file, and enter the following JavaScript (if your hello world JavaScript is still there, delete it):

   var myImage = document.querySelector(‘img‘);
   
   myImage.onclick = function() {
       var mySrc = myImage.getAttribute(‘src‘);
       if(mySrc === ‘images/firefox-icon.png‘) {
         myImage.setAttribute (‘src‘,‘images/firefox2.png‘);
       } else {
         myImage.setAttribute (‘src‘,‘images/firefox-icon.png‘);
       }
   }
    
   

   　　

4. Save all files and load index.html in the browser. Now when you click the image, it should change to the other one!

So here, we are storing a reference to our image element in the myImage variable. Next, we make this variable‘s onclick event handler property equal to an anonymous function. Now, every time this image element is clicked:

1. We retrieve the value of the image‘s src attribute.
2. We use a conditional to check whether the src value is equal to the path to the original image:
   1. If it is, we change the src value to the path to the 2nd image, forcing the other image to be loaded inside the <image> element.
   2. If it isn‘t (meaning it must already have changed), we change the src value back to the original image path, to flip it back to how it was originally.

Supercharging our example website

原文：http://www.cnblogs.com/hephec/p/4601145.html