Javascript compare 3 values

You could shorten that to

if(g === h && g === f && g !== null)
{
//do something
}

For an actual way to compare multiple values (regardless of their number)
(inspired by/ simplified @Rohan Prabhu answer)

function areEqual(){
   var len = arguments.length;
   for (var i = 1; i< len; i++){
      if (arguments[i] === null || arguments[i] !== arguments[i-1])
         return false;
   }
   return true;
}

and call this with

if( areEqual(a,b,c,d,e,f,g,h) )
{
//do something
}

And a more recent approach

function areEqualNotNull(values) {
  if (values[0] === null) return false;

  return values.every(value => value === values[0]);
}