Why did not he define the html?

You're correct. I looked at the solution file provided and he does not declare or initialize the html variable. JavaScript is pretty smart and if the variable to be used is global (outside a function and in our main code) it can sort of figure it out itself. Remember our discussion on scope?

Take a look at this short example:

var x = 20;
y = 5;

console.log(x * y);

Now, you might suspect that this will generate an error, but it won't. It actually logs 100 to the console. Most programming languages require that you set up your variable and declare it before you use it. JavaScript is a little more forgiving. That being said, it's considered best practice to declare your variables before you use them. Hope this helps