User Guide

Conditional constructs 29
Both Lingo and JavaScript syntax provide conventions for altering the default execution order or
script statements, and for performing actions depending on specific conditions. For example, you
may want to do the following in your scripts:
• Execute a set of statements if a logical condition is true, or execute alternate statements if the
logical condition is false.
• Evaluate an expression and attempt to match the expression’s value to a specific condition.
• Execute a set of statements repeatedly until a specific condition is met.
Testing for logical conditions
To execute a statement or set of statements if a specified condition is true or false, you use the
if...then...else (Lingo) or if...else (JavaScript syntax) structures. For example, you can
create an
if...then...else or if...then structure that tests whether text has finished
downloading from the Internet and, if it has, then attempts to format the text. These structures
use the following pattern to test for logical conditions:
• In both Lingo and JavaScript syntax, statements that check whether a condition is true or false
begin with the term
if.
• In Lingo, if the condition exists, the statements following the term then are executed. In
JavaScript syntax, curly brackets (
{ }) take the place of the Lingo term then, and must
surround each individual
if, else, or else if statement.
• In both Lingo and JavaScript syntax, if the condition does not exist, scripts skip to the next
statement in the handler using the term
else or else if.
• In Lingo, the term end if specifies the end of the if test. In JavaScript syntax, the if test ends
automatically, so there is no term that explicitly ends the test.
To optimize your script’s performance, test for the most likely conditions first.
The following statements test several conditions. The term
else if specifies alternative tests to
perform if previous conditions are false:
-- Lingo syntax
if _mouse.mouseMember = member(1) then
_movie.go("Cairo")
else if _mouse.mouseMember = member(2) then
_movie.go("Nairobi")
else
_player.alert("You’re lost.")
end if
// JavaScript syntax
if (_mouse.mouseMember = member(1)) {
_movie.go("Cairo");
}
else if (_mouse.mouseMember = member(2)) {
_movie.go("Nairobi");
}
else {
_player.alert("You’re lost.");
}