jQuery: put a default value in all empty textboxes

_{Textbox refers to <input type="text"> in this question.}

For each textbox with a given class i would li开发者_Python百科ke to check if the value equals '', and if it does I want to make the value '0'. I would like to do this as soon as the page is loaded.

This is the closest I've got now:

$(document).ready(function() {
  if ($('.myclass').val() == '') $('.myclass').val('0');
})

The problem here is that this code will give all my textboxes (with class="myclass") the value '0' as soon as one of them is empty. I know this is the expected behaviour given the code I use now, but I'm pretty new to jQuery and I haven't really got the hang of the selectors yet. How would I solve this? Do I need to create a separate function to do the check on one element and then call that for each of the elements that apply to the selector? If so, how would I do this?

In jQuery 1.4, a function can be passed to val() that will be executed on all elements in the collection:

$(document).ready(function() {
  $('.myclass').val(function (index, value) {
    // If the element has a value, return it, else return "0"
    return value || "0";
  });
});

Example

For versions older than jQuery 1.4, you need to use .each() on the collection:

$(document).ready(function() {
    $('.myclass').each(function() {
        this.value = this.value || "0";
    });
});

Example

This might be the simplest answer:

$("input.myclass[value=]").val("0");

Only elements with no value get selected. This works because the value attribute reflects the text the user put in.

Try

$(document).ready(function() {
  $('.myclass[type=checkbox]').each(function(){
      if($(this).val()=='')
          $(this).val('0');
    });
})

$(document).ready( function() {
  $('input:checkbox').each( function() {
    // check the val
    if( $(this).val()=='')
      // do something
  });
});