for loop in checkboxes js

Hello, How I can write the following code in a for loop?


if (theF.red.checked) {

cost += parseFloat(theF.red.value);

}

if (theF.yellow.checked) {

cost += parseFloat(theF.yellow.value);

}

if (theF.blue.checked) {

cost += parseFloat(theF.blue.value);

}

Code:

---

var colors = ['red', 'yellow', 'blue'];
for (var i = 0; i < colors.length; i++) {
    if (theF[colors[i]].checked)
        cost += parseFloat(theF[colors[i]].value);
}


---

thanks a lot for the help.. but if I have to process unknown number of elements ?