Comparing forEach() and reduce() for summing an array of numbers in JavaScript.

We are required to compare the time taken respectively by the ES6 functions forEach() and reduce() for summing a huge array of numbers.

As we can't have a huge array of numbers here, we will simulate the magnitude of array by performing the summing operation for large number of times (iterations)

Example

Let's write the code for this −

const arr = [1, 4, 4, 54, 56, 54, 2, 23, 6, 54, 65, 65];
const reduceSum = arr => arr.reduce((acc, val) => acc + val);
const forEachSum = arr => {
   let sum = 0;
   arr.forEach(el => sum += el);
   return sum;
};
const iterations = 1000000000;
console.time('reduce');
for(let i = 0; i < iterations; i++){
   let sumReduce = reduceSum(arr);
};
console.timeEnd('reduce');
console.time('forEach');
for(let j = 0; j < iterations; j++){
   let sumForEach = forEachSum(arr);
};
console.timeEnd('forEach');

Output

Following is the output in the console −

reduce: 19.058s
forEach: 45.204s

So roughly, the ratio of time taken by Array.prototype.reduce() to the time taken by Array.prototype.forEach is  1 : 1.4

AmitDiwan

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Updated on: 15-Sep-2020

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