If you want to know hz of your monitor

getHz.js

/// Complexity can't be less than 3 because sometimes happens lags and can get incorrect value, so minimal is 3, not less
async function getHz(complexity, approach) {
    complexity = (complexity < 3 ? 3 : complexity) || 5;
    approach = approach || "average";
    let arr = [];
    while (arr.length < complexity) {
        let value = Math.floor(
            await new Promise((resolve, reject) => {
                requestAnimationFrame((time1) => requestAnimationFrame((time2) => resolve(1000 / (time2 - time1))));
            })
        );
        arr.push(value);
    }

    /// approach #1 count the most amount repeats
    function getMax(arr) {
        let item = 0;
        let count = 0;
        arr.reduce((acc, el) => {
            acc[el] = (acc[el] || 0) + 1;
            item = acc[el] >= count ? (count++, el) : item;
            return acc;
        }, {});

        return item;
    }
    
    /// approach #2 sort and get number standing in the middle
    function getAverage(arr){
        arr = arr.sort((a, b) => {
            return a > b ? 1 : -1 
        });
        return arr[Math.floor(arr.length / 2)];
    }
    return (approach === "average") ? getAverage(arr) : (approach === "counting") ? getMax(arr) : getAverage(arr);
}