var availableTags = [
"ActionScript",
"AppleScript",
"Asp",
"BASIC",
"C",
"C++",
"Clojure",
"COBOL",
"ColdFusion",
"Erlang",
"Fortran",
"Groovy",
"Haskell",
"Java",
"JavaScript",
"Lisp",
"Perl",
"PHP",
"Python",
"Ruby",
"Scala",
"Scheme"
];
$("#auto").autocomplete({
source: availableTags,
change: function (event, ui) {
$("input[type='submit']").prop("disabled", !ui.item);
}
});
<form>
<input type="text" id="auto" />
<input type="submit" disabled="disabled" />
</form>
External resources loaded into this fiddle: