how to pause timer or freeze it and resume -> javascript

I am doing a little app in javascript that has some timers around. At some point I need to change the variables that a single timer is using during runtime.

I tried a coiple of times just changing the variable (incrementing it, for instance in 10 units) still the timer will have a weird behavior. So I figured out that the timer must be stopped first, change the variable and after that resume it (but still dunno this is possible).

What I want to ask is: there is any way to pause a timer function and then resume it?

EDIT: the variables are not local for the timer (they are global)

var t1;
t1 =setTimeout("dosomethig",1000) //1000 = 1 sec

clearTimeout(t1); // to release timeout