User Guide

Scripting syntax 13
• Parentheses are required after all method and function names. For example, when calling the
Sound object’s
beep() method, you must include the parentheses after the word beep.
Otherwise, a script error will occur.
// JavaScript syntax
_sound.beep(); // this statement will work properly
_sound.beep; // this statement will result in a script error
When you call a method, function, or handler from within another method, function, or
handler, you must include parentheses in the calling statement. In the following example, the
modifySprite() method contains a call to a spriteClicked handler. The call to the
spriteClicked handler must include parentheses; otherwise, a script error occurs.
// JavaScript syntax
function modifySprite() {
spriteClicked(); // this call to the handler will work properly
spriteClicked; // this call to the handler results in a script error
}
function spriteClicked() {
// handler code here
}
You can also use parentheses to override the order of precedence in math operations, or to
make your statements easier to read. For example, the first math expression below yields a
result of 13, while the second expression yields a result of 5:
5 * 3 - 2 -- yields 13
5 * (3 - 2) -- yields 5
• Event handler syntax varies between Lingo and JavaScript syntax. In Lingo, handlers use the
syntax
on handlerName. In JavaScript syntax, handlers are implemented as functions, and use
the syntax
function handlerName(). For example, the following statements comprise a
handler that plays a beep when the mouse button is clicked:
-- Lingo syntax
on mouseDown
_sound.beep()
end
// JavaScript syntax
function mouseDown() {
_sound.beep();
}
• Event handler parameter syntax can vary between Lingo and JavaScript syntax. Both Lingo and
JavaScript syntax support enclosing parameters passed to a handler within parentheses. If more
than one parameter is passed, each parameter is separated by a comma. In Lingo, you can also
pass parameters that are not enclosed by parentheses. For example, the following
addThem
handler receives the two parameters
a and b.
-- Lingo syntax
on addThem a, b -- without parentheses
c = a + b
end
on addThem(a, b) -- with parentheses
c = a + b
end
// JavaScript syntax
function addThem(a, b) {
c = a + b;
}