Random Numbers Array not working in the javascript

i have javascript Array

var Numbers = [ 1,2,3];
document.write (Numbers[ Math.floor( Math.random( ) * 3 ) ] );

i want to put it into the URL Like this:

"//connect.facebook.net/en_US/all.js#xfbml=1&appId= + Numbers + ";

i want to show random numbers after appId=