GraphQLDate.js

// Based on https://gist.github.com/langpavel/b30f3d507a47713b0c6e89016e4e9eb7
const serializeDate = value => {
	if (value instanceof Date) {
		return value.toJSON().slice(0, 10)
	} else if (typeof value === 'number') {
		return Math.trunc(value)
	} else if (typeof value === 'string') {
		return (new Date(value)).toJSON().slice(0, 10)
	}
	return null
}

const parseDate = value => {
	if (value == null) {return null}

	try {
		return new Date(value)
	} catch (err) {
		return null
	}
}

const parseDateFromLiteral = ast => {
	if (ast.kind === Kind.INT) {
		return parseDate(Number(ast.value))
	} else if (ast.kind === Kind.STRING) {
		return parseDate(ast.value)
	}
	return null
}

export const DateType = new GraphQLScalarType({
	name: 'Date',
	description:
		'A date without time (or timezone)',
	serialize: serializeDate,
	parseValue: parseDate,
	parseLiteral: parseDateFromLiteral,
})