WordPress - Enqueue scripts for only if LT IE 9

Question

In a WordPress theme, how do you conditionally include scripts for ie8 and below? This is primarily to apply polyfills for various html5/css3 features. I see that wp has the $is

Answer 1

Solution for WordPress 4.2 and above

The correct way would be to apply wp_enqueue_script since it JavaScripts here, and not css styles. Also, it is better to use get_bloginfo('stylesheet_url') to make sure this also works in Child Themes.

/**
 * IE Fallbacks
 */

function load_IE_fallback() {
    wp_register_script( 'ie_html5shiv', get_bloginfo('stylesheet_url'). '/js/html5shiv.min.js', __FILE__, false, '3.7.2' );
    wp_enqueue_script( 'ie_html5shiv');
    wp_script_add_data( 'ie_html5shiv', 'conditional', 'lt IE 9' );

    wp_register_script( 'ie_respond', get_bloginfo('stylesheet_url'). '/js/respond.min.js', __FILE__, false, '1.4.2' );
    wp_enqueue_script( 'ie_respond');
    wp_script_add_data( 'ie_respond', 'conditional', 'lt IE 9' );
}
add_action( 'wp_enqueue_scripts', 'load_IE_fallback' );