Visualforce Page Values Erased on ReRender

Question

I have a VF page set up for users to enter one or more Opportunity Products from a custom search. I also have a script set up to default the Quantity field to "1". The problem I am running into is that if a user changes the Quantity to anything but "1", when a new product is added to the list my VF page ReRenders and the value of the Quantity is then reset back to "1". Does anyone know how I can update my script to populate "1" if the Quantity field is empty and use the value already entered in the Quantity field if it is not empty?

VF Line:

<apex:inputField value="{!s.Quantity}" style="width:70px" required="true" id="qty">
    <script>
        document.getElementById('{!$Component.qty}').value = 1;
    </script>
</apex:inputField>

Answer 1

When you reRender an area with a script block, the script gets run again. This means that it'll always reset the value back to 1. As such, you should probably check its value first:

<apex:inputField value="{!s.Quantity}" style="width:70px" required="true" onkeyup="refreshTotals();" id="qty">
    <script>
        if(!document.getElementById('{!$Component.qty}').value) {
            document.getElementById('{!$Component.qty}').value = 1;
        }
    </script>
</apex:inputField>

This isn't the only way to do it, but is the method that would require the least amount of effort from where your code is right now.

Answer 2

There's not enough code here to determine the issue. My hunch is that refresh totals includes a call to an action method that contains a rerender attribute referencing a parent element of this field. When you combine that with your JS you are guarenteeing the field will be set back to 1. There's about a dozen ways to set the default value of the field to 1 without using JS.

For instance, when you instantiate the object within the controller for the first time, you can set it to 1 within the controller so that it appears as 1 by default. That should set the default to 1 only on page load only, unless you set it in the same method you call when you rerender (which would be silly).

Here is a rough example:

Apex Class

public class pageController {
    public OpportunityLineItem s {
        get {
            if (s == null) {
                s = new OpportunityLineItem();
                s.quantity = 1;
            }

            return s;
        }

        set;
    }
}

One of the issues I see most common in new SF devs is that they are more fammiliar with Javascript then apex/visualforce and default to JS to accomplish tasks in the way that they're used to/understand. In this case, JS is not the answer.