var a = 4, b;
if(a==1) { b = 'a is one'; }
else if(a==2) { b = 'a is two'; }
else if(a==3) { b = 'a is three'; }
else if(a==4) { b = 'a is four'; }

var a = 4, b;
switch(a) {
  case 1: b = 'a is one'; break;
  case 2: b = 'a is two'; break;
  case 3: b = 'a is three'; break;
  case 4: b = 'a is four'; break;
}