Iterating over javascript arrays | Performance comparison [https://gists.cwidanage.com/2019/11/how-to-iterate-over-javascript-arrays.html]

array_performance.js

const { PerformanceObserver, performance } = require('perf_hooks');

let arraySize = 1000000;
let iterations = 100;

console.log("Starting performance test with %d array size and %d iterations", arraySize, iterations);

let values = {
    FORIN: 0,
    FOROF: 0,
    FOREACH: 0,
    JUST_FOR: 0
}

const obs = new PerformanceObserver((items) => {
    let entry = items.getEntries()[0];
    console.log(entry.name, entry.duration);
    values[entry.name] += entry.duration;
    performance.clearMarks();
});
obs.observe({ entryTypes: ['measure'] });

function generateArray() {
    let arr = [];
    for (let i = 0; i < arraySize; i++) {
        arr[i] = 'val' + i;
    }
    return arr;
}



for (let i = 0; i < iterations; i++) {
    let arr = generateArray();


    //foreach
    performance.mark('A');
    arr.forEach((val) => {
        let x = val + 1;
    });
    performance.mark('B');
    performance.measure('FOREACH', 'A', 'B');


    //For In
    performance.mark('A');
    for (const val in arr) {
        let x = val + 1;
    }
    performance.mark('B');
    performance.measure('FORIN', 'A', 'B');

    //For Of
    performance.mark('A');
    for (const val of arr) {
        let x = val + 1;
    }
    performance.mark('B');
    performance.measure('FOROF', 'A', 'B');

    //Just for
    performance.mark('A');
    for (let i = 0; i < arr.length; i++) {
        let x = arr[i] + 1;
    }
    performance.mark('B');
    performance.measure('JUST_FOR', 'A', 'B');
}


console.log(Object.entries(values).sort((a, b) => {
    return a[1] - b[1];
}).map(obj => {
    obj[1] /= iterations;
    return obj;
}));