Mocha before() & beforeEach() execution order with nested describe()

before.js

'use strict';

describe('mocha before hooks', function () {
	before(() => console.log('*** top-level before()'));
	beforeEach(() => console.log('*** top-level beforeEach()'));
	describe('nesting', function () {
		before(() => console.log('*** nested before()'));
		beforeEach(() => console.log('*** nested beforeEach()'));
		it('is a nested spec', () => true);
	});
});

//   mocha before hooks
// *** top-level before()
//     nesting
// *** nested before()
// *** top-level beforeEach()
// *** nested beforeEach()
//       ✓ is a nested spec
//
//
//   1 passing (8ms)

Thanks for this. I was trying to access a nested object property within the nested describe block and getting a TypeError because the beforeEach hook in the top-level describe, where the object was being assigned, was not being called prior to that so the object was in fact undefined.

before

describe('top-level', () => {
  let obj;

  beforeEach(() => {
    obj = {
      nested: {
        property: 'value'
      }
    };
  });

  describe('nested', () => {
    obj.nested.property = 'new-value';
  });
});

after

describe('top-level', () => {
  let obj;

  beforeEach(() => {
    obj = {
      nested: {
        property: 'value'
      }
    };
  });

  describe('nested', () => {
    beforeEach(() => {
      obj.nested.property = 'new-value';
    });
  });
});

this was very helpful!

Thank you!

top level beforeEach initializes something that is used by the nested before

From the example above the nested before() is called before the top level beforeEach().

So if the nested before() relies on the top level beforeEach() to initialize something, the result might be undefined or null