JSFiddle - React, Tailwind, and code Playground

JavaScript

let arr = ["test.email+alex@leetcode.com","test.e.mail+bob.cathy@leetcode.com","testemail+david@lee.tcode.com"];

var numUniqueEmails = function(emails) {
	var parts;
  var emailStr;
  var uniqueCount = 0;
  var emailsMap = {};
  
  for (let i = 0; i < emails.length; i++) {
		parts = emails[i].split('@');
    
    emailStr = parts[0].split('+')[0].replace(/\./g, '') + '@' + parts[1]
    if (!emailsMap[emailStr]) {
    	emailsMap[emailStr] = true;
      uniqueCount++;
    }
  }
  
  return uniqueCount;
};

console.log(numUniqueEmails(arr));