Is it any better solution to insert inline javascript to post or page. Currently I am using 3rd party Inline Javascript Plugin, everything works well. But I am fear that it will causing security leak, is this true?

Once you enter the world of PHP, it is really hard to go back to using Javascript, but they still serve their purpose. If you can replace a Javascript with PHP code, tags, or script in WordPress, do so. Your life will be much easier. If not, here are a few tips to make your Javascript work in WordPress.
http://codex.wordpress.org/Using_Javascript