WMLScript-Specific Literals and Operators

WMLScript supports several literals that are not included in JavaScript. The invalid value is one of them. When you divide a number by zero, you get the invalid value. You also get it if an operation results in a floating-point number that is not part of the set of finite real numbers supported by the single-precision floating-point format. In fact, any data type conversion failure results in a returned value of invalid.

The typeof operator in JavaScript returns a string representing the variable type. In WMLScript, this operator return an integer value:

The intrinsic function isvalid returns true if the type of the expression is valid, false if the expression is not valid. The following example demonstrates the new token:

var str = "Doc JavaScript";
var ok = isvalid(str);  // true
var tst = isvalid(1/0); // false

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