Angular introduced $watchGroup in version 1.3 using which we can watch multiple variables, with a single $watchGroup block
$watchGroup takes array as first parameter in which we can include all of our variables to watch.
$scope.$watchGroup(['var1','var2'],function(newVals,oldVals){
console.log("new value of var1 = " newVals[0]);
console.log("new value of var2 = " newVals[1]);
console.log("old value of var1 = " oldVals[0]);
console.log("old value of var2 = " oldVals[1]);
});