datetype.js

import { GraphQLScalarType } from 'graphql'
import { GraphQLError } from 'graphql/error'
import { Kind } from 'graphql/language'

function coerceDate (value) {
  if (!(value instanceof Date)) {
    // Is this how you raise a 'field error'?
    throw new Error('Field error: value is not an instance of Date')
  }
  if (isNaN(value.getTime())) {
    throw new Error('Field error: value is an invalid Date')
  }
  return value.toJSON()
}

export default new GraphQLScalarType({
  name: 'DateTime',
  serialize: coerceDate,
  parseValue: coerceDate,
  parseLiteral (ast) {
    if (ast.kind !== Kind.STRING) {
      throw new GraphQLError('Query error: Can only parse strings to dates but got a: ' + ast.kind, [ast])
    }
    let result = new Date(ast.value)
    if (isNaN(result.getTime())) {
      throw new GraphQLError('Query error: Invalid date', [ast])
    }
    if (ast.value !== result.toJSON()) {
      throw new GraphQLError('Query error: Invalid date format, only accepts: YYYY-MM-DDTHH:MM:SS.SSSZ', [ast])
    }
    return result
  }
})