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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.
Signature:
protected doClassValidation_(newValue: T): T | null | undefined;
Parameters
| Parameter |
Type |
Description |
| newValue |
T |
The value to be validated. |
Returns:
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.
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Last updated 2024-09-18 UTC.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Missing the information I need","missingTheInformationINeed","thumb-down"],["Too complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2024-09-18 UTC."],[[["\u003cp\u003e\u003ccode\u003edoClassValidation_\u003c/code\u003e is a method used to validate changes to a field's value before it's set, allowing subclasses to implement custom validation logic.\u003c/p\u003e\n"],["\u003cp\u003eThe method can return \u003ccode\u003eT\u003c/code\u003e to set a modified value, \u003ccode\u003enull\u003c/code\u003e to reject the change and trigger an error, or \u003ccode\u003eundefined\u003c/code\u003e to accept the value as is.\u003c/p\u003e\n"],["\u003cp\u003eSubclasses like \u003ccode\u003eFieldDropdown\u003c/code\u003e can override this method to perform specific validation checks.\u003c/p\u003e\n"],["\u003cp\u003e\u003ccode\u003edoClassValidation_\u003c/code\u003e receives the new value as input and returns instructions on how to proceed with setting the field's value based on the validation outcome.\u003c/p\u003e\n"]]],[],null,["[blockly](./blockly.md) \\\u003e [Field](./blockly.field_class.md) \\\u003e [doClassValidation_](./blockly.field_class.doclassvalidation__1_method.md)\n\nField.doClassValidation_() method\n---------------------------------\n\nValidate the changes to a field's value before they are set. See \\*\\*FieldDropdown\\*\\* for an example of subclass implementation.\n\n\\*\\*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`.\n\n**Signature:** \n\n protected doClassValidation_(newValue: T): T | null | undefined;\n\nParameters\n----------\n\n| Parameter | Type | Description |\n|-----------|------|----------------------------|\n| newValue | T | The value to be validated. |\n\n**Returns:**\n\nT \\| null \\| undefined\n\nOne of three instructions for setting the new value: `T`, `null`, or `undefined`.\n\n- `T` to set this function's returned value instead of `newValue`.\n\n- `null` to invoke `doValueInvalid_` and not set a value.\n\n- `undefined` to set `newValue` as is."]]
