Testing JavaScript Interactively
September 20, 1996
Sometimes it's handy to test a bit of JavaScript without writing a program. An undocumented feature of Netscape
is a command line that allows you to do just that. Just type mocha: or javascript: in the URL box
and you'll be presented with a command-line interface. You can type any JavaScript command, define variables,
and so on. The result of each command or expression you type is shown in the upper frame. Follow
this link to try it out.
(This feature is described in more detail on Pages 255-257 of
Web Workshop: JavaScript)
The JavaScript Test Console
Unfortunately, MSIE doesn't support a similar command line, so this technique is useless for comparing results with
different browsers. I've created a solution called the JavaScript Test Console. This is
very similar to Netscape's built-in command line, but works with any JavaScript-capable browser. Use the URL below
to access the test console:
Features
This is a freeware utility for testing JavaScript statements and
expressions in Netscape 2.0, Netscape 3.0, or MSIE 3.0. It can be used
online at the URL above or copied to your local machine.
The JavaScript Test Console works with both Netscape (2.0
or 3.0) and MSIE 3.0; it also provides slightly neater output including the
command that produced the output. Basically, it's a quick way to test a few
statements without creating an HTML file.
You may find this useful for:
- Testing statements such as alert("hello") in real time
- Checking if properties (such as navigator.userAgent) exist or displaying their values
- observing differences between MSIE and Netscape
Using the JavaScript Test Console
TO USE IT: Type something in the blank and press the "Test Expression"
button. If you type a command, it will be executed; if you type an
expression, it will be evaluated. The command and result for the last 8
expressions are displayed in the upper frame.
TO STEAL IT: You'll need to save copies of these three files, and keep them
in the same directory:
- jsprompt.html (frameset)
- prompt.html (bottom frame)
- blank.html (top frame)
(the top frame is blank, but MSIE doesn't support about:blank)
The JavaScript Test Console is copyrighted, but freely available. Feel free
to use it, put it online on your own server, or modify it. Please contact
me via email if you have made any useful modifications to it; I may want to include
them myself. The only thing you can't do is claim you wrote it.
How it Works
To see the JavaScript source for the Test Console, view the source of the prompt.html file. This simply
uses the eval function to evaluate or execute the commands or expressions you type in the form. The rest of the code
keeps track of the most recent 8 commands, and displays them with their results (without executing them again) in the upper frame.
michael moncur ... jsbooks@starlingtech.com