How can I load certain JavaScripts only on blog pages?

1. Properly enqueue the scripts, via callback hooked into the appropriate hook
2. Use contextual conditional tags to determine when to enqueue

For example, you’d do something like:

function wpse135482_enqueue_scripts() {
    // Only enqueue this script on single post pages
    if ( is_singular( 'post' ) ) {
        wp_enqueue_script( $args );
    }
}
add_action( 'wp_enqueue_scripts', 'wpse135482_enqueue_scripts' );

Further reading:

• wp_enqueue_script()
• is_singular()/is_single()