WMLScript Primer: WMLScript-Specific Literals and Operators


WMLScript Primer

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:

TypeCode
Integer0
Floating Point1
String2
Boolean3
Invalid4

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

Next: How to construct compilation units and pragmas

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Produced by Yehuda Shiran and Tomer Shiran

Created: May 22, 2000
Revised: June 11, 2000

URL: http://www.webreference.com/js/column62/3.html