delegate.m

//
//  AppDelegate.m
//  Webkit2Test
//
//  Created by Koen Bok on 08/08/14.
//  Copyright (c) 2014 Koen Bok. All rights reserved.
//

#import "AppDelegate.h"

@interface AppDelegate ()

@property (weak) IBOutlet NSWindow *window;

@end

@implementation AppDelegate
            
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
    // Insert code here to initialize your application
    
    NSView *contentView = self.window.contentView;
    WKWebView *webView = [[WKWebView alloc] initWithFrame:contentView.frame];
    
    NSString *path = @"/Users/koen/Desktop/Poop.framer";
    NSURL *pathUrl = [NSURL fileURLWithPath:path isDirectory:YES];
    NSString *indexPath = [path stringByAppendingPathComponent:@"index.html"];
    
    [webView loadHTMLString:[NSString stringWithContentsOfFile:indexPath encoding:NSUTF8StringEncoding error:nil] baseURL:pathUrl];
    
    [contentView addSubview:webView];
    
}

- (void)applicationWillTerminate:(NSNotification *)aNotification {
    // Insert code here to tear down your application
}

@end

Error

08/08/14 00:22:51,000 kernel[0]: Sandbox: com.apple.WebKit(4702) deny file-issue-extension <path>/my-script.js