Learning WML, and WMLScript

The Conditional Operator

The conditional operator in WMLScript selects between two subexpressions depending on the result of a condition expression. Its syntax is:

            condition-expression ? true-expression : false-expression

The condition-expression is converted to a Boolean value, and if this results in true the result is the true-expression, and the false-expression isn’t evaluated. If the condition gives Boolean false or can’t be converted, the result is the false-expression, and the true-expression isn’t evaluated. Neither the true-expression nor the false-expression are converted in any way. The result of the conditional operator is of the same type as the selected subexpression.

Note that:

a = b ? c : d;

always has exactly the same effect as:

if (b) {
    a = c;
} else {
    a = d;
}

(Using the conditional operator is usually slightly more efficient than using if and else, however.)

For example:

true ? "yes" : "no" gives string "yes"

false ? "yes" : "no" gives string "no"

invalid ? "yes" : "no" gives string "no"

true ? 1/2 : 1/0 gives floating-point 0.5

false ? 1/2 : 1/0 gives invalid

true ? "" : foo( ) gives string "" and doesn’t call foo( )

Multiple Side Effects

The effect of an expression with multiple side effects to the same variable isn’t explicitly defined in WMLScript. This includes the classic example:

x = x++

(Here, the variable x is incremented as a result of the ++ operator but is also assigned to by the = operator.)

Don’t write code like this. Its behavior varies from browser ...