https://www.franken.de/user/plugins/simplesearch/js/simplesearch.js

1((function(){
2    if (!Element.prototype.matches) {
3        Element.prototype.matches = Element.prototype.msMatchesSelector || Element.prototype.webkitMatchesSelector;
4    }
5    var findAncestor = function(el, selector) {
6        while ((el = el.parentElement) && !((el.matches || el.matchesSelector).call(el, selector))) {}
7        return el;
8    };
9
10    var fields = document.querySelectorAll('input[name="searchfield"][data-search-input]');
11    Array.prototype.forEach.call(fields, function(field) {
12        var form = findAncestor(field, 'form[data-simplesearch-form]'),
13            min = field.getAttribute('data-min') || false,
14            location = field.getAttribute('data-search-input'),
15            separator = field.getAttribute('data-search-separator');
16
17        if (min) {
18            var invalid = field.getAttribute('data-search-invalid');
19            field.addEventListener('keydown', function() {
20                field.setCustomValidity(field.value.length >= min ? '' : invalid);
21            });
22        }
23
24        form.addEventListener('submit', function(event) {
25            event.preventDefault();
26
27            if (field.checkValidity()) {
28                window.location.href = location + separator + field.value;
29            }
30        });
31    });
32})());