jQuery单选按钮：checked和$（this）.parent

Question

The radio button is checked by default when the page loads. I want the label that wraps around this radio button to have a CSS class added to it.

What's wrong with my code?

JSFIDDLE: http://jsfiddle.net/3ar43086/4/

$(document).ready(function() {
    if ($('input[type=radio]').is(':checked')) {       
    $(this).parent('label').addClass('checked'); }      
});

<label for="myRadio"><input type="radio" id="myRadio" value="Example Radio Button" name="amount" checked>Example Radio Button</label>

.checked { background: yellow; }

Answer 1

$(this) in your code refers to document instead of the input .

This fixes it:

$(document).ready(function() {
  if ($('input[type=radio]').is(':checked')) {            
    $('input[type=radio]').parent('label').addClass('checked'); 
  }
});

You could also do it like this:

$(document).ready(function() {
  $('input[type=radio]:checked').parent('label').addClass('checked'); 
});

Answer 2

this in the following line refers to window

$(this).parent('label').addClass('checked');

You should do this instead:

$(document).ready(function() {
    var myInput = $('input[type=radio]');
    if (myInput.is(':checked')) {       
    myInput.parent('label').addClass('checked'); }      
});

Or, if you want to treat all the input on your page:

$(document).ready(function() {
    $('input[type=radio]').each(function(){
        if ($(this).is(':checked')) {       
            $(this).parent('label').addClass('checked');
        }      
    });
});