TinyMCE wordpress, custom button does not show up - wordpress

Question

I created a plugin in wordpress to add a button to the TinyMCE. I have at the moment the code below which follows very strictly the example here:
https://www.gavick.com/blog/wordpress-tinymce-custom-buttons#tc-section-1
Php file
< ? php
/*
Plugin Name: TinyMCE Custom Buttons
Plugin URI:
Description:
Version:
Author:
Author URI:
License:
License URI:
*/
//Hook the button on init, so after loading wordpress
add_action('init', 'add_button1234');
//add filters within th function which loads after loading wordpress
function add_button1234() {
// add new buttons
add_filter('mce_buttons', 'myplugin_register_buttons1234');
// Load the TinyMCE plugin
add_filter('mce_external_plugins', 'register_1234');
}
//Add the newly created button to ithe $buttons array
function register_1234($buttons) {
array_push($buttons, 'separator', 'button1234');
return $buttons;
}
//create the button
function myplugin_register_tinymce_javascript1234($plugin_array) {
$plugin_array['button1234'] = plugins_url('plugin.js', __FILE__);
return $plugin_array;
}
?>
javascript file
(function() {
tinymce.PluginManager.add('button1234', function(editor, url) {
editor.addButton('button1234', {
text: 'My test button',
icon : false,
onclick : function() {
editor.insertContent('Hello World!');
}
});
});
})();
Also when I follow exactly the code from the site (only adapting the JS url, it doesn't work.) What could I possible have done wrong?

Answer 1

It looks like you might not be calling the right function when adding the filter mce_buttons in the add_button1234() function.
Change this line:
add_filter( 'mce_buttons', 'myplugin_register_buttons1234' );
To:
add_filter( 'mce_buttons', 'myplugin_register_tinymce_javascript1234' );