ReferenceError : Can't find variable Safari

I am developing a simple Safari Extension and i have a manifest json file to inject a script into my web page. When the extension is running, it gives an error **ReferenceError: can't find variable safari".

What could be the issue if anyone has an idea on creating extensions in Safari. I converted my firefox extension to Safari extension using Xrun from Xcode.

manifest.json

"content_scripts":
[
  {
    "matches": ["*://localhost/*"],
    "all_frames": true,
    "js": ["jquery.js"],
    "run_at": "document_idle"
  }
]

jquery.js

console.log('Test');
console.log(safari);