How to store response body in supertest?

I am testing very basic REST api with supertest. I want to save the item id received in response body and assign it to a variable. Using this id i want to make further tests like get-item-by-id or update-item-by-id. No official documentation has covered this so a beginner friendly answer would be very helpful.

test i have written

const request = require("supertest")
let id;

describe('Products API', () => {
    it('GET  /products --> array of products', async () => {
        return request('http://localhost:3001')
            .get('/api/products')
            .expect(200)
            .expect('Content-Type', /json/)
            .then(response => {
                expect(response.body).toEqual(
                    expect.objectContaining({
                        success: true,
                        data: expect.any(Array)
                    })
                )
            })
    })

})

Answer

Use regular JS variables

const request = require("supertest")

describe('Products API', () => {
    it('GET  /products --> array of products', async () => {
        return request('http://localhost:3001')
            .get('/api/products')
            .expect(200)
            .expect('Content-Type', /json/)
            .then(response => {
                expect(response.body).toEqual(
                    expect.objectContaining({
                        success: true,
                        data: expect.any(Array)
                    })
                )
                const data = response.body.data;

                expect(data.length).toBeGreaterThan(0)

                data.forEach(product => {
                    let id = product.id;
                    // expect data about the products
                }) 
            })
    })

})

want to make further tests like get-item-by-id or update-item-by-id

You should explicitly test those endpoints, not via GET /api/products

E.g.

it('POST /products/{id} --> Updates a product', async () => {
  const id = 1;
  const result = request('http://localhost:3001')
    .post(`/api/products/${id}`)
    ...

  // TODO: Check the product was actually updated in the database, for example
});

More importantly, don’t (or try not to) store variable state between tests.