BeatNik BeatNik - 1 month ago 15
Javascript Question

Chai-related error message: "AssertionError: expected undefined to deeply equal"

I wrote a function that when given a list of objects and an
id, returns the same list, but with the corresponding object marked active
(all other objects should not be active).

const list = [
{ id: 1, active: false },
{ id: 2, active: false },
{ id: 3, active: true },
{ id: 4, active: false }
];

function markActive(list, value) {
list.forEach((id) => {
if (id.active = (id.id === value)) {
return true;
} else {
return false;
}
});
}

markActive(list, 2);
console.log(list)


Returns:

[ { id: 1, active: false },
{ id: 2, active: false },
{ id: 3, active: false },
{ id: 4, active: true } ]


It's working like a charm, except when I run "npm run [filename]" I get an error message:

Running Tests for [filename].
------------
[ { id: 1, active: false },
{ id: 2, active: false },
{ id: 3, active: false },
{ id: 4, active: true } ]


markActive
1) Case 1 (Given Sample)
2) Case 2 (String IDs)


0 passing (16ms)
2 failing

1) markActive Case 1 (Given Sample):
AssertionError: expected undefined to deeply equal [ { id: 1,
active: false },
{ id: 2, active: true },
{ id: 3, active: false },
{ id: 4, active: false } ]
at Function.assert.deepEqual
(node_modules/chai/lib/chai/interface/assert.js:216:32)
at Context.it (tests/test_02.js:23:12)

2) markActive Case 2 (String IDs):
AssertionError: expected undefined to deeply equal [ { id: '1',
active: false },
{ id: '2', active: true },
{ id: '3', active: false },
{ id: '4', active: false } ]
at Function.assert.deepEqual
(node_modules/chai/lib/chai/interface/assert.js:216:32)
at Context.it (tests/test_02.js:40:12)


Any idea what I'm doing wrong? Here's the code that sets up the tests:

const chai = require("chai");
const sinon = require("sinon");
const assert = chai.assert;

const markActive = require("../answers/02.js");

describe("markActive", () => {

it("Case 1 (Given Sample)", () => {
var list = [
{ id: 1, active: false },
{ id: 2, active: false },
{ id: 3, active: true },
{ id: 4, active: false }
];
var newList = markActive(list, 2);
var targetList = [
{ id: 1, active: false },
{ id: 2, active: true },
{ id: 3, active: false },
{ id: 4, active: false }
];
assert.deepEqual(newList, targetList);
});

it("Case 2 (String IDs)", () => {
var list = [
{ id: "1", active: false },
{ id: "2", active: false },
{ id: "3", active: true },
{ id: "4", active: false }
];
var newList = markActive(list, "2");
var targetList = [
{ id: "1", active: false },
{ id: "2", active: true },
{ id: "3", active: false },
{ id: "4", active: false }
];
assert.deepEqual(newList, targetList);
});

});

Answer

Your function isn't returning anything, so any variables you try to set to the result will be set as undefined.

To fix this, simply add a return statement to the end of your function.

function markActive(list, value) {
  list.forEach((id) => {
    if (id.active = (id.id === value)) {
      return true;
    } else {
      return false;
    }
  });

  return list; // return the updated list
}

NOTE: It's worth mentioning that because the array is referenced, you're modifying the values in-place. This is why the array you defined outside the function still had updated results even though you weren't logging the returned value. This can have unintended side effects if you were to run the markActive() function several times on the same list. If you want a new list to be returned, look into ways of copying and deep copying arrays in Javascript.

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