blockly > Field > doClassValidation_

Field.doClassValidation_() method

Validate the changes to a field's value before they are set. See **FieldDropdown** for an example of subclass implementation.

**NOTE:** Validation returns one option between T, null, and undefined. **Field**'s implementation will never return undefined, but it is valid for a subclass to return undefined if the new value is compatible with T.


protected doClassValidation_(newValue: T): T | null | undefined;


Parameter Type Description
newValue T The value to be validated.


T | null | undefined

One of three instructions for setting the new value: T, null, or undefined.

  • T to set this function's returned value instead of newValue.

  • null to invoke doValueInvalid_ and not set a value.

  • undefined to set newValue as is.