Mocha 'this' in before and beforeEach hooks

Question

The following test code, written using Mocha.js fails. I expect the someVal to be increased 3 times and equal 3 in the last test. The issue came up in more complex scenario where I used value set in outer before block to set up another in inner beforeEach block. Simplified case:

describe('increasing 3 times', function() {
  before(function() {
    this.instanceThis = this;
    return this.someVal = 0;
  });
  beforeEach(function() {
    return this.someVal += 1;
  });
  return describe('going deeper', function() {
    before(function() {
      return this.someVal += 1;
    });
    beforeEach(function() {
      return this.someVal += 1;
    });
    return it('has increased someVal to 3', function() {
      return this.someVal.should.equal(3);
    });
  });
});

Answer 1

this is not what you think it is. this gets redefined in every function() {} block (unless Mocha calls them in some specific way I'm not familiar with).

What you want is to use scope in your advantage:

describe('increasing 3 times', function() {
  var someVal; // Initialization.
  before(function() {
    someVal = 0; //No need to return from before()
  });
  beforeEach(function() {
    someVal += 1;
  });
  describe('going deeper', function() {
    before(function() {
      someVal += 1;
    });
    beforeEach(function() {
      someVal += 1;
    });
    return it('has increased someVal to 3', function() {
      someVal.should.equal(3);
    });
  });
});

Also, you don't need to return so much. In fact, you almost never have to return in test code.