dns: refactor and use validators

The logical NOT operator and validators should be used where
appropriate.

lib/internal/dns/promises.js

@@ -28,7 +28,6 @@ const {
   QueryReqWrap
 } = internalBinding('cares_wrap');
 const {
-  ERR_INVALID_ARG_TYPE,
   ERR_INVALID_ARG_VALUE,
   ERR_MISSING_ARGS,
 } = codes;
@@ -44,7 +43,7 @@ function onlookup(err, addresses) {
     return;
   }
 
-  const family = this.family ? this.family : isIP(addresses[0]);
+  const family = this.family || isIP(addresses[0]);
   this.resolve({ address: addresses[0], family });
 }
 
@@ -61,7 +60,7 @@ function onlookupall(err, addresses) {
 
     addresses[i] = {
       address,
-      family: family ? family : isIP(addresses[i])
+      family: family || isIP(addresses[i])
     };
   }
 
@@ -107,8 +106,8 @@ function lookup(hostname, options) {
   var verbatim = getDefaultVerbatim();
 
   // Parse arguments
-  if (hostname && typeof hostname !== 'string') {
-    throw new ERR_INVALID_ARG_TYPE('hostname', 'string', hostname);
+  if (hostname) {
+    validateString(hostname, 'hostname');
   } else if (options !== null && typeof options === 'object') {
     hints = options.hints >>> 0;
     family = options.family >>> 0;
@@ -242,15 +241,15 @@ Resolver.prototype.reverse = resolver('getHostByAddr');
 Resolver.prototype.resolve = function resolve(hostname, rrtype) {
   var resolver;
 
-  if (typeof rrtype === 'string') {
+  if (rrtype !== undefined) {
+    validateString(rrtype, 'rrtype');
+
     resolver = resolveMap[rrtype];
 
     if (typeof resolver !== 'function')
       throw new ERR_INVALID_ARG_VALUE('rrtype', rrtype);
-  } else if (rrtype === undefined) {
-    resolver = resolveMap.A;
   } else {
-    throw new ERR_INVALID_ARG_TYPE('rrtype', 'string', rrtype);
+    resolver = resolveMap.A;
   }
 
   return ReflectApply(resolver, this, [hostname]);