The attr() is a method which either returns or set selected elements values and attributes An attribute value must be a string whereas a property can be of any type. prop() methods gets the property value for the first element in the given matched set. A property is in the DOM while attribute is in the HTML that is parsed into DOM.

<input blah="hello">

Add a below code inside your script

function myfunc()
{
   return '<hr/>.prop: ' + $('input').prop('param') + '<br/>' +
          '.attr: ' + $('input').attr('param') + '<br/><hr/>';
};

var html = myfunc();

$('input').prop('param', 'pear');
$('input').attr('param', 'apple');

html = html + myfunc();

$('body').html(html);

The output will come .

prop: undefined
.attr: hello

and

.prop: pear
.attr: apple

Another example is with the style parameter.

<input style="font:arial;"/>

.attr('style') -- returns inline styles for the matched element i.e. "font:arial;"
.prop('style') -- returns an css style declaration.