{"id":19018466,"date":"2026-09-12T15:35:35","date_gmt":"2026-09-12T15:35:35","guid":{"rendered":"https:\/\/wordpress.org\/support\/?post_type=topic&p=19018466"},"modified":"2026-09-12T16:14:41","modified_gmt":"2026-09-12T16:14:41","slug":"dropdown-js-callback-is-not-a-function-on-repeat-focus","status":"publish","type":"topic","link":"https:\/\/wordpress.org\/support\/topic\/dropdown-js-callback-is-not-a-function-on-repeat-focus\/","title":{"rendered":"dropdown.js callback is not a function on repeat focus"},"content":{"rendered":"\n

Bug: dropdown.js<\/code> \u2014 load_tlib()<\/code> throws “callback is not a function” on repeat focus\/hover<\/strong><\/p>\n\n\n\n

Affected asset:<\/strong> https:\/\/cdn.gtranslate.net\/widgets\/latest\/dropdown.js<\/code> (the “dropdown” widget variant; other variants may share the same helper \u2014 worth checking float.js<\/code> \/ dwf.js<\/code> \/ globe.js<\/code> too).<\/p>\n\n\n\n

Root cause<\/strong><\/p>\n\n\n\n

load_tlib(callback)<\/code> is defined as a general-purpose helper that lazy-injects lib.min.js<\/code> and then runs a callback once it’s loaded:<\/p>\n\n\n\n

function load_tlib(callback){
  if(!window.gt_translate_script){
    window.gt_translate_script = document.createElement('script');
    gt_translate_script.src = 'https:\/\/cdn.gtranslate.net\/widgets\/latest\/lib.min.js';
    document.body.appendChild(gt_translate_script);
    if(callback) gt_translate_script.addEventListener('load', callback, {once:true});
  } else {
    callback && callback();
  }
}<\/code><\/pre>\n\n\n\n
But it is also registered directly as a native DOM event listener:<\/p>\n\n\n\n
e.addEventListener('pointerenter', load_tlib);
e.addEventListener('focusin', load_tlib);<\/code><\/pre>\n\n\n\n
When the browser invokes an event listener, it always passes the triggering Event<\/code> object as the argument. So on every focusin<\/code>\/pointerenter<\/code> fired this way, callback<\/code> inside load_tlib<\/code> is actually a native Event<\/code>, not a function.<\/p>\n\n\n\n
    \n
  • First call<\/strong> (window.gt_translate_script<\/code> not yet set): goes into the if<\/code> branch. gt_translate_script.addEventListener('load', callback, {once:true})<\/code> is called with callback<\/code> = an Event<\/code> object. Per the addEventListener<\/code> spec this is silently ignored (no crash, but also no real “on load” callback ever gets registered).<\/li>\n\n\n\n
  • Any subsequent call<\/strong> on the same wrapper (user re-focuses or re-hovers the widget after the first interaction): window.gt_translate_script<\/code> now exists, so execution hits the else<\/code> branch: callback && callback();<\/code>. callback<\/code> is again a truthy Event<\/code> object, so this attempts to invoke the Event<\/code> instance as a function \u2014 which throws:<\/li>\n<\/ul>\n\n\n\n
    Uncaught TypeError: callback is not a function<\/code><\/pre>\n\n\n\n
    Steps to reproduce<\/strong><\/p>\n\n\n\n
      \n
    1. Load a page with the dropdown widget using default settings (url_structure: 'none'<\/code>, so the interaction-based lazy-load path runs).<\/li>\n\n\n\n
    2. Move keyboard focus into the widget’s wrapper element once, or hover it with a pointer once \u2014 no error; window.gt_translate_script<\/code> gets set on this first pass.<\/li>\n\n\n\n
    3. Move focus\/hover away and then back onto the wrapper a second time (or trigger focusin<\/code>\/pointerenter<\/code> on it again in any way) \u2014 Uncaught TypeError: callback is not a function<\/code> is thrown from the callback && callback();<\/code> line inside load_tlib<\/code>.<\/li>\n\n\n\n
    4. This repeats on every subsequent focus\/hover cycle on the same page load.<\/li>\n<\/ol>\n\n\n\n
      Suggested fix<\/strong><\/p>\n\n\n\n
      load_tlib<\/code> is used both as a plain callback-style helper (e.g. called manually inside doGTranslate<\/code> with a real function) and directly as a native event listener \u2014 these two calling conventions are incompatible without normalizing the argument. Either:<\/p>\n\n\n\n
        \n
      • (a) Wrap it before attaching as a listener, so it’s never invoked with the native Event<\/code> as its argument: e.addEventListener('focusin', () => load_tlib());e.addEventListener('pointerenter', () => load_tlib());<\/code><\/li>\n\n\n\n
      • (b) Or guard the type inside load_tlib<\/code> itself, so any non-function argument is ignored instead of crashing: if (typeof callback === 'function') callback(); <\/code>(and the same guard before the addEventListener('load', callback, ...)<\/code> call).<\/li>\n<\/ul>\n\n\n\n
        Either change is small, localized to load_tlib<\/code>, and doesn’t affect the widget’s public config\/settings.<\/p>\n","protected":false},"template":"","class_list":["post-19018466","topic","type-topic","status-publish","hentry"],"jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/wordpress.org\/support\/wp-json\/wp\/v2\/topic\/19018466","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wordpress.org\/support\/wp-json\/wp\/v2\/topic"}],"about":[{"href":"https:\/\/wordpress.org\/support\/wp-json\/wp\/v2\/types\/topic"}],"version-history":[{"count":1,"href":"https:\/\/wordpress.org\/support\/wp-json\/wp\/v2\/topic\/19018466\/revisions"}],"predecessor-version":[{"id":19018480,"href":"https:\/\/wordpress.org\/support\/wp-json\/wp\/v2\/topic\/19018466\/revisions\/19018480"}],"wp:attachment":[{"href":"https:\/\/wordpress.org\/support\/wp-json\/wp\/v2\/media?parent=19018466"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}