Creating an email custom scalar to Apollo GraphQL

In this tutorial i will show how to implement an Email custom scalar to Apollo GraphQL.

Implement an email scalar isn’t a hard task but i will show in details.

You must implement the functions __parseValue, __serialize and __parseLiteral.

We need a regex to check the email, in this tutorial i used this one:

First we must implement the __parseValue function. Basically we will just test the input type and check the input with our Regex:

After this we will implement the __serialize function , in our example let’s just return the value:

And finally lets implement the __parseLiteral function , we will check the literal kind and check our regex with literal value:

And that’s it ! Our email custom scalar is done. You can check the complete code and the unit test below:

	import { gql } from 'apollo-server-express'
	import { GraphQLError } from 'graphql/error'
	import { Kind } from 'graphql/language'
	const EMAIL_REGEX = new RegExp(
	/^[a-zA-Z0-9.!#$%&’*+/=?^_`{|}~-]+@[a-zA-Z0-9-]+(?:\.[a-zA-Z0-9-]+)*$/
	)
	const Email = gql`
	"Scalar data representing email"
	scalar Email
	`
	/* eslint-disable no-underscore-dangle */
	export const resolver = {
	Email: {
	__parseValue(value) {
	if (typeof value !== 'string') {
	throw new TypeError('Value is not string')
	}
	if (!EMAIL_REGEX.test(value)) {
	throw new TypeError(`Value is not a valid email address: ${value}`)
	}
	return value
	},
	__serialize(value) {
	return value
	},
	__parseLiteral(ast) {
	if (ast.kind !== Kind.STRING) {
	throw new GraphQLError(
	`Value is not string : ${ast.kind}`
	)
	}
	if (!EMAIL_REGEX.test(ast.value)) {
	throw new GraphQLError(`Value is not a valid email address: ${ast.value}`)
	}
	return ast.value
	}
	}
	}
	export default () => [
	Email
	]

view raw email-scalar-type.js hosted with ❤ by GitHub

	import { Kind } from 'graphql/language'
	import { resolver } from '../src/graphql/schema/types/scalar/email'
	/* eslint-disable no-underscore-dangle */
	const email = 'test@test'
	const emailComplete = '[e-mail]'
	describe('Email scalar', () => {
	describe('when email is valid', () => {
	it('serialize correctly with complete email', () => {
	expect(resolver.Email.__serialize(emailComplete))
	.to
	.eql(emailComplete)
	})
	it('serialize correctly', () => {
	expect(resolver.Email.__serialize(email))
	.to
	.eql(email)
	})
	it('parseValue correctly with complete email', () => {
	expect(resolver.Email.__parseValue(emailComplete))
	.to
	.eql(emailComplete)
	})
	it('parseValue correctly', () => {
	expect(resolver.Email.__parseValue(email))
	.to
	.eql(email)
	})
	it('parseLiteral correctly with complete email', () => {
	expect(
	resolver.Email.__parseLiteral({
	value: emailComplete,
	kind: Kind.STRING
	}, {})
	)
	.to
	.eql(emailComplete)
	})
	it('parseLiteral correctly', () => {
	expect(
	resolver.Email.__parseLiteral({
	value: email,
	kind: Kind.STRING
	}, {})
	)
	.to
	.eql(email)
	})
	})
	describe('when email is invalid', () => {
	describe('and not a string', () => {
	it('parseValue', () => {
	expect(() => resolver.Email.__parseValue(435))
	.to
	.throw(
	'Value is not string'
	)
	})
	it('parseLiteral', () => {
	expect(() => resolver.Email.__parseLiteral({
	value: '453',
	kind: Kind.INT
	}, {}))
	.to
	.throw('Value is not string : IntValue')
	})
	})
	describe('and not an email address', () => {
	it('parseValue', () => {
	expect(() => resolver.Email.__parseValue('this is a test'))
	.to
	.throw('Value is not a valid email address: this is a test')
	})
	it('parseLiteral', () => {
	expect(() => resolver.Email.__parseLiteral({
	value: 'this is a test',
	kind: Kind.STRING
	}, {}))
	.to
	.throw('Value is not a valid email address')
	})
	})
	})
	})

view raw email-scalar-type_spec.js hosted with ❤ by GitHub

I hope this helps !