dns: lazy loaded

PR-URL: #20567
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>

Author: BridgeAR

lib/dgram.js

@@ -35,7 +35,6 @@ const {
 ERR_SOCKET_DGRAM_NOT_RUNNING
 }=errors.codes;
 const{ Buffer }=require('buffer');
-constdns=require('dns');
 constutil=require('util');
 const{ isUint8Array }=require('internal/util/types');
 constEventEmitter=require('events');
@@ -47,6 +46,9 @@ const { UV_UDP_REUSEADDR } = process.binding('constants').os;
 
 const{UDP, SendWrap }=process.binding('udp_wrap');
 
+// Lazy load for startup performance.
+letdns;
+
 constBIND_STATE_UNBOUND=0;
 constBIND_STATE_BINDING=1;
 constBIND_STATE_BOUND=2;
@@ -72,9 +74,10 @@ function lookup6(lookup, address, callback) {
 
 
 functionnewHandle(type,lookup){
-if(lookup===undefined)
+if(lookup===undefined){
+if(dns===undefined)dns=require('dns');
 lookup=dns.lookup;
-elseif(typeoflookup!=='function')
+}elseif(typeoflookup!=='function')
 thrownewERR_INVALID_ARG_TYPE('lookup','Function',lookup);
 
 if(type==='udp4'){