Custom number to fix (JS)

custom_number_to_fix.js

Number.prototype.customNumberFix = function(fractionalPart) {
    let split = String(this).split('.');
    if (split.length > 1) {
        let left = split[0];
        let right = split[1].substr(0, (!fractionalPart ? 4 : fractionalPart));
        return Number(left + (fractionalPart !== 0 ? `.${right}` : ``));
    }
    return Number(this);
}

//Use
(3223.320020).customNumberFix(2) //result 3223.32