JavaScript - what is the fastest way to sum array elements?

When it comes to performance, the for loop is more efficient than reduce() method.

However, if "the fastest" method means a one-liner for you, use the reduce().

Practical examples

1. Using for loop (the most efficient)

// ONLINE-RUNNER:browser;

const array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

let result = 0;

for (let i = 0; i < array.length; ++i) {
    result += array[i];
}

console.log(result); // 55

2. Using reduce() method (one-liner)

// ONLINE-RUNNER:browser;

const array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

const result = array.reduce((previous, current) => previous + current, 0);

console.log(result); // 55

Performance test

In this section, I've compared two methods of summation:

• sum1() - uses reduce() method,
• sum2() - uses for loop. 

// ONLINE-RUNNER:browser;

const test = (repeats, description, func) => {
    const t1 = Date.now();
    for (let i = 0; i < repeats; ++i) {
        func();
    }
    const t2 = Date.now();
    const dt = t2 - t1;
    console.log(`${description}: totoal time is ${dt} ms`);
};


// Tested algorithms:

const sum1 = (array) => {
    return array.reduce((previous, current) => previous + current, 0);
};

const sum2 = (array) => {
    let count = 0;
    for (let i = 0; i < array.length; ++i) {
        count += array[i];
    }

    return count;
};


// Input array:

const array1 = [
    1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4,
    5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3,
    4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2,
    3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1,
    2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5,
];


// Performance tests:

const repeats = 10000; // set number of repeats depending on cases complexity

test(repeats, 'Using reduce()', () => sum1(array1));
test(repeats, 'Using for loop', () => sum2(array1));

See also

1. JavaScript - test algorithm performance

2. JavaScript - sum array of numbers

References

1. Array.prototype.reduce() - JavaScript | MDN