This adds the aria-expanded and aria-controls attributes to the mobile nav of the Twenty Twelve theme - they currently are not present, ex: ​https://wp-themes.com/twentytwelve/

Trac ticket: https://core.trac.wordpress.org/ticket/62892

@bschneidewind Please use const and let for block-scoped variables (no var).

@bschneidewind Please use const and let for block-scoped variables (no var).

@bschneidewind Please use const and let for block-scoped variables (no var).

@umeshsinghin While that's generally good advice, it's generally WordPress policy to keep things stylistically consistent within the context they're written. Since most of this file uses var to declare variables, it isn't a requirement.

Note the ​JavaScript coding standards, which explicitly indicate that const and let should be used in code written using ES2015 or newer; which is definitely not the case with Twenty Twelve.

It's not a problem to use more modern notations in older files, but not necessary, either.

I think this can be done without declaring new variables by editing the main function (and reusing its button and menu variables). I also recommend setting aria-expanded="false" in the script file in case a child theme overrides the header template.

	// Assign an ID for the default page list if no menu is set as Primary.
	if ( ! menu.id ) {
		menu.setAttribute( 'id', 'twentytwelve-page-list-menu' );
	}

	button.setAttribute( 'aria-controls', menu.id );
	button.setAttribute( 'aria-expanded', 'false' );

	button.onclick = function() {
		if ( -1 === menu.className.indexOf( 'nav-menu' ) ) {
			menu.className = 'nav-menu';
		}

		if ( -1 !== button.className.indexOf( 'toggled-on' ) ) {
			button.className = button.className.replace( ' toggled-on', '' );
			menu.className = menu.className.replace( ' toggled-on', '' );
			button.setAttribute( 'aria-expanded', 'false' );
		} else {
			button.className += ' toggled-on';
			menu.className += ' toggled-on';
			button.setAttribute( 'aria-expanded', 'true' );
		}
	};

Thanks @sabernhardt ~ just adjusted the approach!

Tested and reviewed; lgtm.

In 59911:

In 59912: