Javascript - Use 'if-else' or 'if' only for single value assignment?

I am curious, for the codes blow:

Code 1:

var myValue = 10;
if(isBlocked)
  myValue = 20;

Code 2:

var myValue;
if(isBlocked)
  myValue = 20;
else
  myValue = 10;

Both should do the same thing. But I prefer Code 1, as it obviously requires less lines. Is it better to use Code 1 for single value assignment?