challenge_05.js

const ENTRY_LIST = `PYmt8hd,jdcrLI,jdcrli@gmail.com,27,London
aN21Mhj,yoHrWHE,oHrWHE@example,40,
,oHrWHE,oHrWHE@a.com,a,
2RVxZLzIcs,jvNCJj,jvncjj@hotmail.com,45,Berlin
XUOUmi9,utuPMN,htuPMN@invalid,,Berlin
UXMmi9,htuPMN,@@@.com,,Berlin
Y2FCxmg*E4L,4vZtIH,dvztih@gmail.com,27,London
Y2FgXXE4L,DvZtIH,dvztih@gmail.com,27,London
wYR2DOE,vsWtBk,vsWtBk@example,,Paris
(MIDUni,3vsWtBk,midu@gmail.com,,Barcelona
G1WV7gK,RFHWCi,rfhwci@yahoo.com,53,Sydney
OQc_YTY,bGyjPo,,,BuenosAires
OQc_YTY,eGyjPo,bGyjPo@example,,Caracas
uzHXNR,IFLUDB,ifludb@hotmail.com,46,Madrid
u56gsjt,eBbEBV,eBbEBV@invalid,49,
QH87Wd,fImzHM,fimzhm@gmail.com,38,Madrid
Dhy92jh,pB1P64,pB1P64@hotmail.com,52,CDMX
6DkGW62P,ldmcDE,ldmcde@gmail.com,33,Madrid
B89dht_,nceCp2,nceCp2@invalid,68,Rome
O8TsZ7,jauTbB,jautbb@gmail.com,45,New York
tIR9N,yOkZBg,yokzbg@yahoo.com,68,Tokyo
1KN4ZOe,emuBwK,emubwk@gmail.com,27,London
2efL9,zAPgvK,zapgvk@outlook.com,33,Paris
f9Fw1q6tWq,djrWrL,djrwrl@outlook.com,20,New York
weoFk,prYGAC,hrygac@yahoocom,19,Sydney
mZf2R,LnSBAh,lnsbah@outlook.com,18,Paris
KIuLH,kKpddF,kkpddf@outlook.com,32,Rome
4359Rm,LAlhya,lalhya@outlook.com,62,London
KYQZq9yg,ZTvLpI,ztvlpi@outlook.com,27,Madrid
9hC&UV8,wWZxgp,mwzxgp@yahoo.com,49,Madrid
ra7wsGC,DFgbNn,dfgbnn@yahoo.com,40,New York
0=uUIzOsDN,ngPCGN,jgpcgn@gmail.com,57,Rome
zaor8f,WXQwzY,wxqwzy@yahoo.com,27,Paris
KTMoYqn,ZFSwLp,zfswlp@yahoo.com,57,Berlin
OJMgD,mmJyyc,mmjyyc@yahoo.com,30,Paris
J49HyU,udMyki,udmyki@hotmail.com,35,Rome
ZBiXSV,gQXcjA,gqxcja@yahoo.com,68,Paris
lP6GLm6,ljiCsY,ljicsy@gmail.com,45,Berlin
neZAj,bBIbVF,bbibvf@gmail.com,58,London
9uLq2KwoIr,OWXXBl,owxxbl@outlook.com,46,Sydney
RELT7fgmnD,dplQIl,,58,New York
HDKVi,AxLzOk,axlzok@hotmail.com,68,New York
Mp7lqou9z,SJzlEy,sjzley@gmail.com,63,London
6rDP6BCQv,nnqyAa,nnqyaa@outlook.com,45,New York
OyH2qjKxZ,nwWZuw,nwwzuw@yahoo.com,56,Rome
L8DHMmE44p,MoAcMe,moacme@hotmail.com,67,Paris
TlSmF,fPmepA,fpmepa@outlook.com,42,Rome
E1QH9ci7,hlyLQF,hlylqf@outlook.com,41,New York
mYOpY23,SHmAju,shmaju@hotmail.com,64,Rome
XAEJitTlla,qrpsKE,qrpske@hotmail.com,52,Rome
tS4XE,DoxbRW,doxbrw@outlook.com,26,Tokyo
zGmt6Bg,JXcvKW,jxcvkw@hotmail.com,68,Madrid
4t7td1EpM,cnxBsn,cnxbsn@outlook.com,42,Madrid
USYVWP9,Zhszyq,zhszyq@gmail.com,45,Berlin
xPsBdFX,guBqHO,gubqho@gmail.com,56,Berlin
vjs0muFgD,GlNbyN,glnbyn@hotmail.com,43,Paris
MJjqv,lfmiGU,lfmigu@outlook.com,60,London
jZlHAbXel,YOfnFV,yofnfv@hotmail.com,38,Tokyo
IykL8QNPN,ndBTcB,ndbtcb@gmail.com,28,Berlin
Vq7WI4,CLCYRN,clcyrn@gmail.com,25,Tokyo
utGGulT,RdmXuh,rdmxuh@yahoo.com,68,Rome
FQeos5,aMlzfe,amlzfe@gmail.com,43,Berlin
bJKfMUASk,RnEDLz,rnedlz@outlook.com,36,Berlin
p3GXT0,Meohff,meohff@gmail.com,27,Madrid
TCsiyDQpIl,FdMArs,fdmars@outlook.com,63,Berlin
cb6RRrx,ZCyfir,zcyfir@gmail.com,45,Rome
Fm7V1tR34,VJlNXN,vjlnxn@hotmail.com,32,Rome
VY5EHZHY,EfaHWA,efahwa@outlook.com,25,New York
EkCCjg5e9,JvowjF,jvowjf@outlook.com,68,Paris
KVJd37LC,IzgjKS,izgjks@gmail.com,31,Paris`;

const splitEntryList = ENTRY_LIST.split("\n");

let invalidCases = [];

const isAlphaNumeric = (str) => {
  return /^[a-z0-9]+$/i.test(str) ? true : false;
};

const isEmailFormat = (str) => {
  return /^[a-z0-9]+@[a-z0-9]+\.[a-z0-9]+$/i.test(str) ? true : false;
};

splitEntryList.forEach((entry) => {
  const splittedEntry = entry.split(",");

  // - id: exists and is alphanumeric
  const id = splittedEntry[0];
  if (!id || !isAlphaNumeric(id)) {
    invalidCases.push(entry);
    return;
  }

  // - username: exists and is alphanumeric
  const username = splittedEntry[1];
  if (!username || !isAlphaNumeric(username)) {
    invalidCases.push(entry);
    return;
  }
  // - email: exists and is valid (follows the patter user@domain.com)
  const email = splittedEntry[2];
  if (!email || !isEmailFormat(email)) {
    invalidCases.push(entry);
    return;
  }

  // - location: is optional but if it appears it is a string
  const location = splittedEntry[4];
  if (location && typeof location !== "string") {
    invalidCases.push(entry);
    return;
  }
  // - age: is optional but if it appears it is a number
  const age = Number(splittedEntry[3]);
  if (age && typeof age !== "number") {
    invalidCases.push(entry);
    return;
  }
});

let secretMessage = invalidCases.map((user) => user.split(",")[1][0]).join("");

console.log(secretMessage);