Welcome to the HMTL and JavaScript tester, by Bill Martino.
Here is the help you requested.

HTML and JavaScript Testing On-The-Fly
This set of Web pages will allow you to:

On the HTML side, you can completely rewrite the HTML contents of the page in the right-hand pane. Specifically, it uses the innerHTML property of the BODY element. Simply do the following:
To explore the object model of any page loaded by this web site, do the following: See the heading "Security Restrictions" for limitations on what can be displayed through this facility.

For JavaScript testing, you can enter code and execute it dynamically. You can enter functions, define variables, and enter code to be executed outside of functions. Simply do the following: The JavaScript code from the Text Area is evaluated and run by means of the JavaScript eval() function. This introduces several limitations:

Pre-Defined variables

There are nine pre-defined variables that are part of the JavaScript included in the underlying pages. Since they were read in by the browser when the page was initially loaded, they will stay in memory, and will be accessible to any user-entered scripts. The same names are available in both the left-hand pane and the right-hand pane (via wjm164v.htm), althougth they have different initial values, as shown in the table below.
Initial Value
In left pane
Initial Value
In Right Pane
s1HelloHi There
s2WorldNice Person
d3today's datetoday's date
a1{Bill, Donna, Mike, Devin}{Cain, Abel, Adam, Eve}
a2{53, 46, 18, 16}{6, 13, 29, 37}

Browser Security Restrictions

When loading pages into the right frame or into another window, if all the pages are based on the same server (or on the same computer), then you have reasonably free rein over what your scripts can access and do with those other pages.

However, when a page in the right frame or in another window was loaded from a different server, then the brwoser security restrictions become active and you are very restricted in what your scripts can do. As a general rule, you will have access to the window object , but you can only access a limited subset of its properties and methods.

This restriction can be effectively bypassed by using the File|SaveAs menu selection of the Browser to save the Web page and its supporting files on thge local computer, and then reloading the locally-saved version for examination by the program.