Guide
Extending Factory

Extending a Factory

There may be times when you want to create a new factory that adds properties or variables to an existing factory. In such cases, you can use .def. In the example below, a new employeeFactory is defined by reusing the properties and variables defined in userFactory.

import { factory } from "@factory-js/factory";
 
const userFactory = await factory.define({
  props: {
    name: () => "John",
    age: () => 20,
  },
  vars: {
    title: () => "Mr.",
  },
});
 
// Use `.def` to get the properties and variables from `userFactory`
const { props, vars } = userFactory.def;
 
const employeeFactory = await factory.define({
  props: {
    ...props,
    role: () => "admin",
  },
  vars: {
    ...vars,
    greeting: () => "Hello",
  },
});

Note that the properties and variables returned by .def are those defined at the time of .define. This means that results from method chains using .props or .vars to overwrite values later are not considered. The reason for this is that it is possible to define values dependent on other properties or variables within a method chain, and reusing them is very challenging due to TypeScript limitations.

import { factory } from "@factory-js/factory";
 
const userFactory = await factory
  .define({
    props: {
      name: () => "John",
    },
    vars: {},
  })
  // Here, `name` is overwritten to "Tom", but this is not reflected in the `.def` result
  .props({
    name: () => "Tom",
  });
 
// The `props.name` returned here is "John", not "Tom"
const { props } = userFactory.def;
 
const employeeFactory = await factory.define({
  props: {
    ...props,
    role: () => "admin",
  },
  vars: {},
});
 
console.log(await employeeFactory.build()); // 👉 { name: "John", role: "admin" }
TraitGet Started