Finding average age from array of Objects using JavaScript

Problem

We need to write a JavaScript function that takes an array of objects containing people's data and calculates the average age from the age property.

Example

Following is the code:

const people = [
    { fName: 'Ashish', age: 23 },
    { fName: 'Ajay', age: 21 },
    { fName: 'Arvind', age: 26 },
    { fName: 'Mahesh', age: 28 },
    { fName: 'Jay', age: 19 },
];

const findAverageAge = (arr = []) => {
    const { sum, count } = arr.reduce((acc, val) => {
        let { sum, count } = acc;
        sum += val.age;
        count++;
        return { sum, count };
    }, {
        sum: 0, 
        count: 0
    });
    return (sum / (count || 1));
};

console.log(findAverageAge(people));

Output

23.4

Method 1: Using reduce() (Recommended)

The above example uses reduce() to accumulate both sum and count. Here's a simpler version:

const people = [
    { fName: 'Ashish', age: 23 },
    { fName: 'Ajay', age: 21 },
    { fName: 'Arvind', age: 26 },
    { fName: 'Mahesh', age: 28 },
    { fName: 'Jay', age: 19 }
];

const findAverageAge = (arr) => {
    const totalAge = arr.reduce((sum, person) => sum + person.age, 0);
    return totalAge / arr.length;
};

console.log(findAverageAge(people));

23.4

Method 2: Using for...of Loop

const people = [
    { fName: 'Ashish', age: 23 },
    { fName: 'Ajay', age: 21 },
    { fName: 'Arvind', age: 26 },
    { fName: 'Mahesh', age: 28 },
    { fName: 'Jay', age: 19 }
];

const findAverageAge = (arr) => {
    let totalAge = 0;
    for (const person of arr) {
        totalAge += person.age;
    }
    return totalAge / arr.length;
};

console.log(findAverageAge(people));

23.4

Method 3: Using map() and reduce()

const people = [
    { fName: 'Ashish', age: 23 },
    { fName: 'Ajay', age: 21 },
    { fName: 'Arvind', age: 26 },
    { fName: 'Mahesh', age: 28 },
    { fName: 'Jay', age: 19 }
];

const findAverageAge = (arr) => {
    const ages = arr.map(person => person.age);
    const sum = ages.reduce((total, age) => total + age, 0);
    return sum / ages.length;
};

console.log(findAverageAge(people));

23.4

Handling Empty Arrays

For robust code, handle empty arrays to avoid division by zero:

const findAverageAge = (arr) => {
    if (arr.length === 0) {
        return 0;
    }
    const totalAge = arr.reduce((sum, person) => sum + person.age, 0);
    return totalAge / arr.length;
};

console.log(findAverageAge([])); // Empty array
console.log(findAverageAge([{ fName: 'John', age: 25 }])); // Single person

0
25

Comparison

Conclusion

The reduce() method provides the cleanest solution for calculating average age from an array of objects. Always handle edge cases like empty arrays for production code.