WordPress at a glance
function is not described

network_settings_add_js() WP 4.1.0

Print JavaScript in the header on the Network Settings screen.

No Hooks.

Return

Nothing (null).

Usage

network_settings_add_js();

Code of network settings add js: wp-admin/includes/ms.php WP 5.2.2

<?php
function network_settings_add_js() {
	?>
<script type="text/javascript">
jQuery(document).ready( function($) {
	var languageSelect = $( '#WPLANG' );
	$( 'form' ).submit( function() {
		// Don't show a spinner for English and installed languages,
		// as there is nothing to download.
		if ( ! languageSelect.find( 'option:selected' ).data( 'installed' ) ) {
			$( '#submit', this ).after( '<span class="spinner language-install-spinner is-active" />' );
		}
	});
});
</script>
	<?php
}