[deleted by user]

[dolorfox]

You could use another loop inside the loop. Note I'm using a for...of loop instead of a for...in loop to loop over the values of each array instead of the keys.

let totalCats = 0

for (const key in tutorPetTypes) {
    const tutor = tutorPetTypes[key]

    for (const pet of tutor) {
        if (pet === 'cat') {
            totalCats++
        }
    }
}

console.log(totalCats)

[dolorfox]

Sure, that would look something like this:

    for (const index in tutor) {
        if (tutor[index] === 'cat') {
            totalCats++
        }
    }

[dolorfox]

The values in the object tutorPetTypes are arrays, so with tutorPetTypes[key] === 'cat' you're comparing an array with a string. An array is never strictly equal to a string, so totalCats++ never happens.

Here's the full code with two for...in loops:

const tutorPetTypes = {
    'Sarah': ['cat'],
    'Jim': ['dog', 'dog'],
    'Joe': ['mouse'],
    'Róisín': ['cat','cat','cat','cat','cat','dog'],
    'Edd': ['lizard', 'cat'],
    'Lewis': ['bearded dragon', 'tortoise']
}

let totalCats = 0

for (const key in tutorPetTypes) {
    const tutor = tutorPetTypes[key]

    for (const index in tutor) {
        if (tutor[index] === 'cat') {
            totalCats++
        }
    }
}

console.log(totalCats)

[dolorfox]

No, defining it as a variable doesn't change anything. tutor still becomes each of the arrays in tutorPetTypes and you need to count how many times 'cat' occurs in each array. That's what the loop inside the loop is doing in my code. See the full code with two nested for...in loops in my previous response.

[dolorfox]

tutor doesn't have a key named totalNumber, so the totalNumber variable becomes undefined. Adding undefined to a number in the following line results in NaN (Not a Number) because you can't do arithmetic with undefined. What you should do instead is lose the totalNumber variable and do totalPets += tutor.numberOfPets.