Where and how to put inline js in pages

You can add inline js by using the wp_add_inline_script function.

function prince_scripts() {

    wp_enqueue_script( 'prince-script', get_template_directory_uri(). 'main.js');

    $hide_on_mobile = apply_filters( 'prince_hide_on_mobile', true );

    $data="var hideOnMobile = " . ( $hide_on_mobile ? 'true': 'false' ) . ';';

    wp_add_inline_script( 'prince-script', $data, 'before' );

}

add_action( 'wp_enqueue_scripts', 'prince_scripts');