wp_enqueue_script() filters

theme-functions.php

<?php
/**
 * Functions used be the WordPress theme.
 */

if ( ! function_exists( 'get_google_maps_src' ) ) :
/**
 * Take a Google Maps API v3 key (and optional callback) and return value for the 'src' attribute to load the api script.
 * To be used for getting the wp_enqueue_script() URI parameter.
 *
    // Sample Implementation
    // wp_enqueue_script( 'map_page_scripts', get_google_maps_src( 'AIzaSyCvqaM_Z5_s3BsCYcm268IBzR62JoiW3ko', 'initGoogleMaps' ), array(), false, true );
 *
 * @param  string $key A Google Maps API v3 key generated for this site.
 * @param  string $callback A JavaScript function name for the Google Maps API to call back to initialize the maps on the page.
 * @return string An escaped URL for use by a wp_enqueue_script() function.
 */
function get_google_maps_src( $key = '', $callback = '' )
{
	if ( ! isset( $key ) )
		return;

	$callback = ( isset( $callback ) ) ? '&callback=' . $callback : '';

	return esc_url_raw( sprintf( 'https://maps.googleapis.com/maps/api/js?key=%1$s%2$s', $key, $callback ) );;
}
endif;

if ( ! function_exists( 'add_async_attribute' ) ) :
/**
 * Add 'async' and 'defer' attributs to the html 'script' tag.
 * 
 * @param  string $tag    The raw html $tag as it is received.
 * @param  string $handle The $handle of the current script, e.g. 'rushhour_map_page_scripts'
 * @return string A string which has conditionally had 'async' and 'defer' attributes added to it.
 */
function add_async_attribute( $tag, $handle )
{
	$async_scripts = array( 'map_page_scripts' );

    if ( ! in_array( $handle, $async_scripts ) )
        return $tag;

    return str_replace( ' src', ' async defer src', $tag );
}
endif;