function assertExist () {
    var val = flag(this, 'object');
    this.assert(
        val !== null && val !== undefined
      , 'expected #{this} to exist'
      , 'expected #{this} to not exist'
    );
  }
### .exist

Asserts that the target is not strictly (`===`) equal to either `null` or
`undefined`. However, it's often best to assert that the target is equal to
its expected value.

    expect(1).to.equal(1); // Recommended
    expect(1).to.exist; // Not recommended

    expect(0).to.equal(0); // Recommended
    expect(0).to.exist; // Not recommended

Add `.not` earlier in the chain to negate `.exist`.

    expect(null).to.be.null; // Recommended
    expect(null).to.not.exist; // Not recommended

    expect(undefined).to.be.undefined; // Recommended
    expect(undefined).to.not.exist; // Not recommended

A custom error message can be given as the second argument to `expect`.

    expect(null, 'nooo why fail??').to.exist;

The alias `.exists` can be used interchangeably with `.exist`.

@name exist
@alias exists
@namespace BDD
@api public