Chapter 1

Using JT

• If the program is in a box, right-click and choose 'select all', then 'copy'.

  Move to the JT window, click 'Clear' then paste in the code.

• If the code is not in a box, drag the mouse through it to select it, choose 'copy', then paste to JT as above.

To execute the program, click Run.

Click Trace to step it a line at a time. In the pop-up box, click OK to step to the next instruction. To stop tracing, click Cancel. (A JavaScript error will be shown, for line 200. Ignore this by choosing the No option. Ideally, switch off Javascript errors in your browser)

Click Pretty to format the code neatly.

The display in the top left quarter shows line numbers and variable values. This is refreshed after every assignment statement is executed (i.e. whenever any variable changes). You will use this feature later.

Now we will write some programs.

Displaying Text with print, printLine, and alert

or here******.

function void main() { print("Hello World"); }

Click on the 'Run' button, and note the text that appears in the bottom-right Results area. It is:

Hello World

Here, some introductory points are covered, to be explained in more depth later.

• Line 1 is necessary all JT programs. You don't need to know exactly what it does at this stage.
• Lines 2 and 4 are 'braces' - { } , also known as curly brackets . They group statements together. Note that in JT we also have parentheses (round brackets).
• Line 3 is where the work gets done. The print statement displays any text we enclose between double-quotes.

The semicolon ends every statement - the problem is that every line of the above is not technically a statement so you can't litter semicolons around with abandon. In fact, there is only one statement - the print - in the above.

Note on Browsers

IE is recommended at present. The Mozilla version does not work with blank lines. Put a space on blank lines if you use e Mozilla)