How does the seed work?

[Minozzzi]

Hi guys, I have a question. I want to know how the seed works, when running the tests to generate values.

Thankss :D

[xDivisionByZerox]

Well, seeding a Faker instance with the same value equals in same return values from different instances (or even the same one).

Example:

const one = new Faker(); // for simplicity without actual parameters
const two = new Faker(); // for simplicity without actual parameters

const mySeed = 1337;
one.seed(mySeed);
one.name.firstName(); // Devyn
one.name.firstName(); // Craig

two.seed(mySeed);
two.name.firstName(); // Devyn
two.name.firstName(); // Craig

// reset to get same values "again"
one.seed(mySeed);
one.name.firstName(); // Devyn
one.name.firstName(); // Craig

Stackblitz example

If you need anything more specific, you might want to be more specific on your question.

[xDivisionByZerox]

I have a really hard time following you. We are an open-source project. If you want to see how anything is implemented, you can simply check the source code. In the case of firstName you can simply check the address module.

faker/src/modules/name/index.ts

Lines 84 to 93 in ca7cde5

	firstName(gender?: GenderType): string {
	const { first_name, female_first_name, male_first_name } =
	this.faker.definitions.name;
	return selectDefinition(this.faker, gender, {
	generic: first_name,
	female: female_first_name,
	male: male_first_name,
	});
	}

[xDivisionByZerox]

Maybe this will help you. In the example faker.firstName() // Devyn, the name Devyn is not "generated" from randomly chosen characters, but picked from a (very) long list of names. For English you can find this list of names in the following file:

faker/src/locales/en/name/first_name.ts

Lines 1 to 10 in ca7cde5

	export default [
	'Aaliyah',
	'Aaron',
	'Abagail',
	'Abbey',
	'Abbie',
	'Abbigail',
	'Abby',
	'Abdiel',
	'Abdul',

[Minozzzi]

I saw how its implemented, but on

faker/src/modules/mersenne/twister.ts

Line 168 in ca7cde5

initByArray(initKey: number[], keyLength: number): void {

I don't understand.
Does my question make sense?

[xDivisionByZerox]

Ok, I see (I hope). The file you are referring to is an implementation of a pseudorandom number generator called Mersenne Twister. It's basically a bunch of math that ensures that if you put numbers in (the seed). The same thing comes out but still looks random. If you want to find out more you should read the article I linked to you or generally any other article about random number generation.

But TBH I don't think most users don't need to have that deep of an understanding of how this works, since its high-level mathematics and that's kinda scary.

I really hope this helps (sorry if it doesn't :( ).

[Minozzzi]

Yes, it really makes sense to me. Thanks for answering me. With this lot of calculation it generates the random values of the locations?