Trying to pass a name of some existing variable in order to read it's value

Question

I'm new to JavaScript, hope that someone can point me in the right direction.

var foo = 10;
var bar = "foo";  // I want bar to be a pointer to the contents of foo
alert(bar);   // Naturally, the alert shows 'foo'

How can I setup a pointer to variable foo to let bar show 10 instead of 'foo'