Code (https://github.com/jquery/jquery/blob/master/src/attributes.js#L168):

return (elem.value || "").replace(rreturn, "");

This code assumes that ''elem.value'' will return a String. This is true for most form-related elements, but <meter> and <progress> (both of which have @''value'' and are form-associated) define their ''value''-property as a double. Doubles do not have a ''replace'' method, resulting in a JavaScript error.

Reproduction code:

var meterElement = document.createElement ('meter'),
    jqMeter = $ (meterElement);

meterElement.value = .5;
jqMeter.val ();

Tested in Google Chrome 13 with jQuery 1.6.1.

Two proposed fixes:

1) Force ''elem.value'' to be a string:

return ((elem.value || "") + "").replace(rreturn, "");

2) Add valHooks for both <meter> as <progress> doing the cast:

jQuery.each([ "meter", "progress" ], function() {
    jQuery.valHooks[ this ] = {
        get: function( elem ) {
            // The meter and progress elements define .value as a double
            return elem.value + "";
        }
    };
});

The issue was identified by Wilfred Nas, http://twitter.com/#!/wnas/status/70527764922499074