<fieldset>
    <label for="postImage">Fetaured Image</label>
    <input type="file" name="featured" id="featured" size="50">
    <img name="frontend-image" id="frontend-image" width="150" height="150">
</fieldset>

(function($) {

    $(document).ready( function() {
    var file_frame; // variable for the wp.media file_frame

    // attach a click event (or whatever you want) to some element on your page
    $( '#featured' ).on( 'click', function( event ) {
    event.preventDefault();

    // if the file_frame has already been created, just reuse it
    if ( file_frame ) {
        file_frame.open();
        return;
    }

    file_frame = wp.media.frames.file_frame = wp.media({
        title: $( this ).data( 'uploader_title' ),
        button: {
            text: $( this ).data( 'uploader_button_text' ),
        },
        multiple: false // set this to true for multiple file selection
    });

    file_frame.on( 'select', function() {
        attachment = file_frame.state().get('selection').first().toJSON();

        // do something with the file here
        $( '#featured' ).hide();
        $( '#frontend-image' ).attr('src', attachment.url);
    });

    file_frame.open();
    });
    });

})(jQuery);

function createPost() {

    // fetaured image
    $uploaddir = wp_upload_dir();
    $file = $_FILES['featured'];
    $uploadfile = $uploaddir['path'] . '/' . basename( $file['name'] );
    move_uploaded_file( $file['tmp_name'] , $uploadfile );
    $filename = basename( $uploadfile );
    $wp_filetype = wp_check_filetype(basename($filename), null );
    $attachment = array(
        'post_mime_type' => $wp_filetype['type'],
        'post_title' => preg_replace('/.[^.]+$/', '', $filename),
        'post_content' => '',
        'post_status' => 'inherit',
        'menu_order' => $_i + 1000
        );
    $attach_id = wp_insert_attachment( $attachment, $uploadfile );
    $featured_url = wp_get_attachment_url( $attach_id );

    //Get the ID of currently logged in user to set as post author
    $current_user = wp_get_current_user();
    $currentuserid = $current_user->ID;

    //Get the details from the form which was posted
    $postTitle = $_POST['postTitle'];
    $contentOfPost = $_POST['postContent'] ;
    $postcontentImage = $_POST['frontend-image'] ;
    $postSatus = 'publish'; // 'pending' - in case you want to manually aprove all posts;

    //Create the post in WordPress
    $post_info = array(
        'post_title'        => $postTitle,
        'post_content'      => $contentOfPost,
        'post_status'       => $postSatus ,
        'post_author'       => $currentuserid,
        'post_mime_type'    => $wp_filetype['type'],
        // 'post_mime_type' => $featured_url,
        // 'thumbnail_id'      => $featured_url
    );
    $post_id = wp_insert_post( $post_info );

    update_post_meta($post_id,'_thumbnail_id',$attach_id);
    set_post_thumbnail( $post_id, $attachmentId );

}