Handling errors for Modify and Describe methods in JavaScript – PB Docs 126

Handling errors for Modify and Describe methods in JavaScript

In all environments, including JavaScript, no runtime error
occurs when Describe and Modify try
to access invalid controls or properties in the DataWindow object.
The validity of the argument string is evaluated before the controls
are accessed.


When the string that specifies the control and property to
be accessed is invalid, Modify returns an error string, instead
of the expected value, such as:

You can use the error message to figure out what part of the
string is incorrect. This is most useful when you are testing your
scripts. The error message, which names the line and column number
after which the string was not recognized, may not be helpful after
your application is deployed.


When the string for Describe has an unrecognized
property, Describe‘s return value ends
with an exclamation point (!). It will return as many values as
it recognizes up to the incorrect one.

When you specify a valid property but that property doesn’t
have a value (either because it hasn’t been set or because
its value is an expression that can’t be evaluated), Describe returns
a question mark (?) for that property. The property’s actual
value is null.

note.png Always check for errors

You should include error-checking code that checks for these
return values. Other errors can occur later if you depend on settings
that failed to take effect.

For more information

For more information on syntax and usage, see Describe and Modify in Chapter 9, “Methods for the DataWindow Control.”

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