how to set radio option checked onload with jQuery

This one will cause form.reset() failure:

$('input:radio[name=gender][value=Male]').attr('checked', true);

But this one works:

$('input:radio[name=gender][value=Male]').click();

How about a one liner?

$('input:radio[name="gender"]').filter('[value="Male"]').attr('checked', true);

JQuery has actually two ways to set checked status for radio and checkboxes and it depends on whether you are using value attribute in HTML markup or not:

If they have value attribute:

$("[name=myRadio]").val(["myValue"]);

If they don't have value attribute:

$("#myRadio1").prop("checked", true);

More Details

In first case, we specify the entire radio group using name and tell JQuery to find radio to select using val function. The val function takes 1-element array and finds the radio with matching value, set its checked=true. Others with the same name would be deselected. If no radio with matching value found then all will be deselected. If there are multiple radios with same name and value then the last one would be selected and others would be deselected.

If you are not using value attribute for radio then you need to use unique ID to select particular radio in the group. In this case, you need to use prop function to set "checked" property. Many people don't use value attribute with checkboxes so #2 is more applicable for checkboxes then radios. Also note that as checkboxes don't form group when they have same name, you can do $("[name=myCheckBox").prop("checked", true); for checkboxes.

You can play with this code here: http://jsbin.com/OSULAtu/1/edit?html,output

Say you had radio buttons like these, for example:

    <input type='radio' name='gender' value='Male'>
    <input type='radio' name='gender' value='Female'>

And you wanted to check the one with a value of "Male" onload if no radio is checked:

    $(function() {
        var $radios = $('input:radio[name=gender]');
        if($radios.is(':checked') === false) {
            $radios.filter('[value=Male]').prop('checked', true);
        }
    });