added task solution

[mbruhler]

Hi,
Great work Artem, I can see that you're getting better in JS. Keep it up!

There are some issues with your code that I'd like to discuss together. The detailed explanation is made in comments but here I also want to add that you should use mocks while testing.

It's always a great idea to create __mocks__ folder and create mock data there, then use it as constants in test cases.

For JS part, I can see that you have troubles with using reduce. I supplied you with some examples but you should spend some time on developing your skills using this function. Iterating arrays is very important.

[mbruhler]

Long and hard to read statement. In my opinion it's always a great idea to seperate such logic into function.
Consider separating filtering method into function like this:

function isMenInCentury(p, century) {
    return p.sex === 'm' && Math.ceil(p.died / 100) === century;
}

And then you can use it like this:

const men = century
   ? people.filter((p) => isMenInCentury(p, century))
   : people.filter((p) => p.sex === 'm');

[mbruhler]

Use reduce rather then iterating and assigning to sum. This way you can also inline variable and lower the number of lines in your code.

Consider following code:

return men.reduce((acc, curr) => {
        acc += curr.died - curr.born;
        return acc;
    }, 0) / men.length;

[mbruhler]

Full example code:

function isMenInCentury(p, century) {
    return p.sex === 'm' && Math.ceil(p.died / 100) === century;
}
function calculateMenAverageAge(people, century) {
    const men = century
        ? people.filter((p) => isMenInCentury(p, century))
        : people.filter((p) => p.sex === 'm');
    
    return men.reduce((acc, curr) => {
        acc += curr.died - curr.born;
        return acc;
    }, 0) / men.length;

}

[mbruhler]

Code is hard to read. Consider creating functions that implement filtering logic like so:

function isWomen(p) {
    return  p.sex === 'f';
}
function hasChildren(p, people){
    return !!people.find((p1) => p1.mother === p.name)
}

Usage:

const women = withChildren
        ? people.filter((p) => womenWithChildren(p, people))
        : people.filter((p) => isWomen(p));

[mbruhler]

Use reduce instead and return the sum instead of assigning to variable and using forEach

return women.reduce((acc, curr) => {
    acc += curr.died - curr.born;
    return acc;
}, 0) / women.length;

[mbruhler]

Same as above. Separate filtering logic from code using utility functions.

[mbruhler]

Use reduce like this

return children.reduce((acc, curr) => {
    acc += curr.born - (people.find((m) => m.name === curr.mother)?.born || 0);
    return acc;
}, 0) / children.length;