readline: 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/tty.js

@@ -26,9 +26,11 @@ const net = require('net');
 const{TTY, isTTY }=process.binding('tty_wrap');
 consterrors=require('internal/errors');
 const{ERR_INVALID_FD,ERR_TTY_INIT_FAILED}=errors.codes;
-constreadline=require('readline');
 const{ getColorDepth }=require('internal/tty');
 
+// Lazy loaded for startup performance.
+letreadline;
+
 functionisatty(fd){
 returnNumber.isInteger(fd)&&fd>=0&&isTTY(fd);
 }
@@ -122,15 +124,19 @@ WriteStream.prototype._refreshSize = function() {
 
 // Backwards-compat
 WriteStream.prototype.cursorTo=function(x,y){
+if(readline===undefined)readline=require('readline');
 readline.cursorTo(this,x,y);
 };
 WriteStream.prototype.moveCursor=function(dx,dy){
+if(readline===undefined)readline=require('readline');
 readline.moveCursor(this,dx,dy);
 };
 WriteStream.prototype.clearLine=function(dir){
+if(readline===undefined)readline=require('readline');
 readline.clearLine(this,dir);
 };
 WriteStream.prototype.clearScreenDown=function(){
+if(readline===undefined)readline=require('readline');
 readline.clearScreenDown(this);
 };
 WriteStream.prototype.getWindowSize=function(){