Javascript form specification

I have multiple forms on a web page that were created using JavaScript and I would like to populate a field in the appropriate form with a value (startDate).

I have tried the following code:

oForm = document.forms['bookingform' + fleetID];
oFormElement = oForm.elements['startdate'];
oFormElement.value = startDate;

..开发者_开发问答.but get the error "oForm.elements is null or not an object".

Until now I have been using document.getElementById('startdate').value instead of creating a forms object. Which is the correct approach when specifying which form the value should populate?

form.elements is a plain array. So either you know the index or you have to search for it.

Form = document.forms['bookingform' + fleetID];
oFormElement = oForm.elements[0]; // This is the index of the element
oFormElement.value = startDate;

If you have to search then it's like this:

Form = document.forms['bookingform' + fleetID];
var oFormElement;
for (var i = 0, len = oForm.elements.length; i < len; ++i) {
    if (oForm.elements[i].name == "startdate") {
        oFormElement = oForm.elements[i];
        break;
    }
}
if (oFormElement) {
    oFormElement = oForm.elements[0]; // This is the index of the element
    oFormElement.value = startDate;
} else {
    // crash
}