[Vuejs]-How can I trigger a function inside 'methode' from external javascript in Vue js?

You could have your external javascript set a global variable, and then within your Vue component watch for changes on that global variable, and let that trigger the method call. That might not work reliably though because the global variable might already have been set before vue gets mounted.

Is there more going on in your document.ready than you’ve shown here? Your Vue component’s Mounted hook could possibly serve just as well?