Does wp_localize_script Call a Javascript Function or Simply Pass PHP Parameters to It

wp_localize_script takes an array of data (in PHP) spits out a javascript. It's a way for you to add dynamic data for a specific script to the front end without having to hook into wp_head or wp_footer and echo it out yourself. More over, wp_localize_script outputs your data right above the script you enqueued. Hooking into wp_head or wp_footer won't do that.

wp_localize_script does not call javascript functions. It's a way to do exactly what you want: pass dynamic data from the server side (PHP) to the client side (javascript).

An Example

Your theme needs to take a piece of post meta data and make it accessible to a javascript function.

So you'd hook into wp_enqueue_scripts and do the following...

<?php
add_action( 'wp_enqueue_scripts', 'wpse34008_enqueue' );
function wpse34008_enqueue()
{
    // if we're not on a singular page, bail
    if( ! is_singular() ) return;

    global $post;
    if( empty( $post ) ) $post = get_queried_object();

    // enqueue your script...
    wp_enqueue_script( 'wpse34008-script', 'http://example.com/path/to/script.js' );

    wp_localize_script(
        'wpse34008-script',
        'wpse34008',
        array(
            'meta' => get_post_meta( $post->ID, '_wpse34008_meta', true )
        )
    );
}

Then somewhere the enqueued script.js file, you can get the post meta like this...

// somewhere in the js file
someFunction( wpse34008.meta );

Make sense?