InvertedSwitchStatement.js

// https://developer.mozilla.org/ru/docs/Web/API/ValidityState
var validityState = { valid: false, stepMismatch: true, tooLong: false };

function errorMessage(validity) {
	// Constant goes in expression
	switch (true) {
	// Variable goes in a case clause
	case !validity.valid:
		return 'is not a Number';
	case validity.stepMismatch:
		return 'value does not fit the rules determined by the step attribute';
	case validity.tooLong:
		return 'value does not need to be longer than ...';
	default:
		return 'some error occurred';
	}
}

console.log(errorMessage(validityState));