Try this!

Before reading the rest of this lesson, write a program that makes Reeborg draw a square as illustrated on this image:

Hint

If you do not know how to, select world Alone and review the commands seen in Test driven learning Your program will make use of 2 instructions (functions) and should have 8 lines.

4. Reeborg goes to France

• Quelque chose à déclarer Monsieur. ... Reeborg?
• Je ne parle pas français .... I do not speak French.
• Do you have something to declare?
• Perhaps I should ...

Reeborg is known internationally and travels often. It might be useful to teach him words in a different language. For functions, this can be done using the Javascript keyword var. I like to think of var as creating some variation of the language. However, in programming terms, this is simply known as declaring a variable.

We can do this in either one or two steps.

Note

On line 1 we define a new word and give it a meaning on line 2. On line 3 we do both steps at once. Notice the absence of parentheses. We can then use the new functions names; the old ones still work as we show on the last line.

var forward;
forward = move;
var turnLeft = turn_left;

forward();
turnLeft();
move();

Try it!

Choose your own names for move and turn_left and use them to make Reeborg draw a square. If your computer has speakers, you might want to add the instruction sound(true) at the very beginning of your program for a bit of added fun.

Perhaps you could define your own language for giving instructions to Reeborg?

Important

Keywords are names in a programming language that are assigned some special meaning that will be the same independently of who writes the program. Note how the var keyword above appears in a different colour in the Javascript editor: all Javascript keywords will be identified similarly.

4.1. Valid names

Note

If you have learned some Javascript elsewhere, you have seen that the var keyword is not normally required. If you choose the “regular” version of Javascript instead of the strict one, you will see that you can avoid using the var keyword. However, this is considered to be a bad practice.

For now, limit yourselves with names that start with a letter and contain only letters, numbers or the underscore character “_”; a name can not have a space in it - which is why many people use the underscore character to create names that look like many words that would be a phrase; thus, instead of turn left, we can write turn_left. An alternative way to write compound names most often used by Javascript programmers is known as camelCase, where the start of a new word is indicated by an uppercase letter. We gave one such example above with turnLeft.