TypeError: Expect is not a function

Question

Why do I get a TypeError: expect is not a function when running this test file?

I've installed mocha and chai locally and run the test via yarn run test which runs simply "test": "mocha".

var chai = require('chai')
var expect = chai.expect()

describe('Array', function () {
  describe('#indexOf()', function () {
    it('should return -1 when the value is not present', function () {
      expect([1, 2, 3].indexOf(4)).to.be.equal(-1)
    })
  })
})

Solution 1

When setting expect, you need to do this:

var expect = chai.expect

You are evaluating the function with (), which is not correct according to the documentation

Solution 2

You are assigning the result of calling the function chai.expect to your variable chai, which do not make sense.

Instead, you need to assign a reference to this function, like this:

var expect = chai.expect;

(without the parentheses)