我有一个附件id，但我需要一个url。如何从附件对象获取url？

// When an image is selected, run a callback.
frame.on( \'select\', function() {
    // Grab the selected attachment.
    var attachment = frame.state().get(\'selection\').first();
    $(\'#\' + id).val(attachment.id);
}); 

函数将其转换为toJSON。现在它工作了。

jQuery(document).ready(function($) {
var frame;

// Build the choose from library frame.
$(document).on("click", ".upload_image_button", function() {
    var id = $(this).attr(\'id\').replace(\'_b\', \'\');  

    if ( frame ) {
        frame.open();
        return;
    }

    // Create the media frame.
    frame = wp.media.frames.meta_image_frame = wp.media({
        // Tell the modal to show only images.
        library: {
            type: \'image\'
        },
    });

    // When an image is selected, run a callback.
    frame.on( \'select\', function() {
        // Grab the selected attachment.
        attachment = frame.state().get(\'selection\').first().toJSON();
        $(\'#\' + id).val(attachment.url);
    });

    frame.open();
    });
});