Small example of using JavaScript to replace Images

I started to learn the JavaScript scripting language. After several days of special learning. I learned that JavaScript is a prototype-based development language. How is it based on the prototype? Despite checking a lot of information, I am still not very clear about its concept. Today we will not discuss the prototype-based issue,... SyntaxHighlighter. all ();

I started to learn the JavaScript scripting language. After several days of special learning. I learned that JavaScript is a prototype-based development language. How is it based on the prototype? Despite checking a lot of information, I am still not very clear about its concept.
 
Today, we will not discuss the prototype-based problem. We use JavaScript to implement a small example of image replacement.
 
Start as follows:
 
I. design interface:
 
First, prepare two images:

 

Then, add a Table with one row and three columns and design it as follows:
 

 
Ii. Code display:
 
[Html]
 
 
 
 
Partition example