решил, нужно было обернуть в
jQuery(document).ready(function($){
});
Полный код
jQuery(document).ready(function($){
var file_frame;
$('#upload').live('click', function(event) {
event.preventDefault();
// If the media frame already exists, reopen it.
if (file_frame) {
file_frame.open();
return;
}
// Create the media frame.
file_frame = wp.media.frames.file_frame = wp.media({
title: 'Choose Image',
button: {
text: 'Choose Image'
},
multiple: true
});
// When an image is selected, run a callback.
file_frame.on('select', function() {
var selection = file_frame.state().get('selection');
selection.map( function( attachment ) {
attachment = attachment.toJSON();
// Do something with attachment.id and/or attachment.url here
$("#featured-footer-image-container").after("<img src=" +attachment.url+" width='100' height='100'>");
});
});
file_frame.open();
});
});