As nhpatt notes you're not actually calling obj.method here, you're passing it as an argument, which will be called at a later time. Looking at a possible impl

As nhpatt notes you're not actually calling obj.method here, you're passing it as an argument, which will be called at a later time. Looking at a possible implementation of setTimeout makes it clearer: function setTimeout(func, delay) { // wait for the delay to complete.. func(); } Here you can see that when the function is called there's nothing to the left of it.