How can I show input fields only when previous input has a valid value?

Question

I have a form that requires between 3 and 10 text input items. When the form first loads it will show 3 inputs (minimum).

I'd like to efficiently show input rows as the previous row has a valid value (let's assume greater than 3 characters for example). So if you fill out the first 3, you will automatically see a 4th optional input row.

Can you help me loop through this quick list efficiently in jQuery?

HTML:

<input type="text" class="item_1" name="item_1">
<input type="text" class="item_2" name="item_2">
<input type="text" class="item_3" name="item_3">
<input type="text" class="item_4" name="item_4">
<input type="text" class="item_5" name="item_5">
<input type="text" class="item_6" name="item_6">
<input type="text" class="item_7" name="item_7">
<input type="text" class="item_8" name="item_8">
<input type="text" class="item_9" name="item_9">
<input type="text" class="item_10" name="item_10">

CSS:

.item_4,.item_5,.item_6,.item_7,.item_8,.item_9,.item_10 { display:none }

Answer 1

This is pretty simple - you shouldn't even need a loop if you let jQuery's chaining do the work. I'd do something like:

$("#myform input").change(function(){ //If an input in your form is changed,
    if ($(this).val() == 42){ //replace with your validation logic :)
         $(this).next('input').show(); //This shows the next sibling element to the triggering element
    } else { //but if it fails validation...
         $(this).nextAll('input').hide().val(""); //hide them and delete the contents to stop the form from uploading invalidated data!
    }
});

This does what you asked, and for bonus points it hides and empties later boxes if their predecessors are later changed to be invalid.