Rewrite admin/includes/js/admin.js without using jQuery.

[itpixelz]

I have rewritten the entire code of admin/includes/js/admin.js in VanillaJS without using any library like jQuery. #10

There is some portion of the code which I found of no use so I did not write it, let me know if that is still required, as I have doubled checked in the Settings page and that is working fine without using this portion of the code as below.

$( function() {
		$( 'body.options-general-php select#WPLANG' ).each( function() {
			$( this ).find( 'option[selected="selected"]' ).removeAttr( 'selected' );
			var val = bogo.defaultLocale || 'en_US';
			val = ( 'en_US' == val ? '' : val );
			$( this ).find( 'option[value="' + val + '"]' ).first().attr( 'selected', 'selected' );
		} );
	} );

[takayukister]

This is admin.js that is used only on admin pages, and only a few latest versions of major browsers are allowed to access WordPress admin screen, so you can and should use modern JS coding more aggressively. You don't have to care about backward compatibility for legacy browsers that doesn't support ES2015.

Some points where you can improve the code are:

1. Use const and let instead of var. This is also mentioned in the WordPress coding standard.

2. Use querySelector() and querySelectorAll() where available. All getElementById() can be replaced to them.

3. Use IIFE.

function init_bogo_admin() {
  ...
}

init_bogo_admin();

This can be written with IIFE as:

( function() {
  ...
} )();

4. Don't use XMLHttpRequest directly. You can use wp.apiFetch to trigger REST API requests.

5. When you code something that manipulates DOM tree, always put it inside a DOMContentLoaded event function.

6. For consistency, avoid using on(action) properties for events. Use addEventListener() instead.

[itpixelz]

I will submit the code in a couple of days with the implementation of TypeScript to match it with the latest coding trends and to match the suggestions above.