You would need to include your JS file (I assume you use Odoo v8).

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
        <template id="assets_backend" inherit_id="web.assets_backend">
            <xpath expr="." position="inside">
                <script type="text/javascript" src="/your_module_name/static/src/js/test.js"></script>
            </xpath>
        </template>
    </data>
</openerp>

Just not going deeper for this example we will select button by text inside it (not the best practice ofcourse). The code below is your test.js file content.

$(document).on('click', $('button:has(span:contains(Text Inside Button))'), function() {
    console.log('call function here');
});