Validators

This is a validation library that provides typed objects from unknown objects.

const validator = new SchemeValidator({
	id: new NumberValidator({ allowCoercion: true })
});

// allowCoercion in NumberValidator allows the conversion of '1' to 1.
// I.e. String numbers are converted to numbers.
const result = validator.validate('query', { id: '1' });
if (!result.isValid()) {
	return;
}

const coerced = result.asCoerced();

const id: number = coerced.id; // allowed
const anyObject = coerced.info; // type error. 'info' is not a member of coerced.

All validators return a result object which has two methods, isValid and asCoerced. asCoerced will throw if isValid is false.

Example

SchemeValidator is the validator used for objects. It attempts to validate the input object based on the shape of the validators object given to the constructor.

const validator = new SchemeValidator({
	id: new NumberValidator({ allowCoercion: true }),
	arg_field: new SetValidator(['dog' as const, 'cat' as const, 1 as const, 2 as const])
});

const resultOne = validator.validate('query', { id: '1' });

// Throws CoercionError. Missing 'arg_field'.
try {
	const coercedOne = resultOne.asCoerced();
} catch (e) {
	if (e instanceof CoercionError) {
		console.log(resultOne.errors);
	} else {
		throw e;
	}
}

const resultTwo = validator.validate('query', { id: '1', arg_field: 'dog' });
const coercedTwo = result.asCoerced();

// Type of arg_field
const arg_field: 'dog' | 'cat' | 1 | 2 = coercedTwo.arg_field;

Const Inference for Set Validator

Set validator takes an array of items and checks if the input field is exactly one of the values in the array; checked using ===.

It can be nice if you write ['dog', 'cat', 1, 2] and the output type is Array<'dog' | 'cat' | 1 | 2>. This can be achieved two ways.

Use const on each element.

// type is Array<'dog' | 'cat' | 1 | 2>
const validator = new SetValidator(['dog' as const, 'cat' as const, 1 as const, 2 as const]);

Alternitively, use const on the entire array if every element in the array should be interpreted as literal const.

// type is Array<'dog' | 'cat' | 1 | 2>
const validator = new SetValidator(['dog', 'cat', 1, 2] as const);

Test

Test config generated by ts-jest.

npx ts-jest config:init

Run tests with npm run test.