feat: add the only validator

docs/validators.md

@@ -83,5 +83,16 @@ validator.custom(
 
         return null;
     },
-)
+);
+```
+
+## only
+
+The only validator allow you to make a validator optional based on a condition.
+
+```js
+validators.only(
+    (values, errors, context) => values?.answer === 42,
+    validators.requiredString('anotherValue'),
+);
 ```

src/OnlyValidator.ts

@@ -0,0 +1,26 @@
+import Context from './Context';
+import Validator from './Validator';
+
+export type OnlyChecker<TOuterContext> = (values: any, errors: any, context: Context<TOuterContext>) => boolean;
+
+class OnlyValidator<TOuterContext = any> extends Validator<TOuterContext> {
+    protected check: OnlyChecker<TOuterContext>;
+
+    protected validator: Validator<TOuterContext>;
+
+    constructor(check: OnlyChecker<TOuterContext>, validator: Validator<TOuterContext>) {
+        super();
+        this.validator = validator;
+        this.check = check;
+    }
+
+    public execute(values: any, errors: any, context: Context<TOuterContext>): any {
+        if (this.check(values, errors, context)) {
+            return this.validator.execute(values, errors, context);
+        }
+
+        return errors;
+    }
+}
+
+export default OnlyValidator;

src/methods.ts

@@ -6,3 +6,4 @@ export { default as RequiredNumber } from './RequiredNumber';
 export { default as RequiredString } from './RequiredString';
 export { default as RequiredValue } from './RequiredValue';
 export { default as CustomValidator } from './CustomValidator';
+export { default as OnlyValidator } from './OnlyValidator';

src/validators.ts

@@ -1,5 +1,6 @@
 import { PropertyPath } from 'lodash';
 import { CustomValidatorHandler } from './CustomValidator';
+import { OnlyChecker } from './OnlyValidator';
 import Validator from './Validator';
 import * as methods from './methods';
 
@@ -26,3 +27,6 @@ export const forEach = <TOuterContext = any>(field: PropertyPath, validator: Val
 
 export const custom = <TOuterContext = any>(field: PropertyPath, validator: CustomValidatorHandler<TOuterContext>) =>
     new methods.CustomValidator<TOuterContext>(field, validator);
+
+export const only = <TOuterContext = any>(check: OnlyChecker<TOuterContext>, validator: Validator<TOuterContext>) =>
+    new methods.OnlyValidator<TOuterContext>(check, validator);