how to separate numbers in javascript

separate numbers in javascript.js

const inpNumber = document.getElementById("my-decimal-number");
inpNumber.addEventListener("keyup", handlerSeparateNumbers)

// functions
function funcReverseString(str) {
    return str.split('').reverse().join('');
}

// event handlers
function handlerSeparateNumbers(e) {
    const thisElement = e.target;
    let thisElementValue = thisElement.value;

    thisElementValue = thisElementValue.replace(/,/g, "");

    if (isNaN(Number(thisElementValue))) {
        alert("لطفا از وارد کردن حروف خودداری فرمایید !")
        return false;
    }

    let seperatedNumber = thisElementValue.toString();
    seperatedNumber = funcReverseString(seperatedNumber);
    seperatedNumber = seperatedNumber.split("");

    let tmpSeperatedNumber = "";

    j = 0;
    for (let i = 0; i < seperatedNumber.length; i++) {
        tmpSeperatedNumber += seperatedNumber[i];
        j++;
        if (j == 3) {
            tmpSeperatedNumber += ",";
            j = 0;
        }
    }

    seperatedNumber = funcReverseString(tmpSeperatedNumber);
    if(seperatedNumber[0] === ",") seperatedNumber = seperatedNumber.replace("," , "");
    thisElement.value = seperatedNumber;
}

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