Solution.js

const numUniqueEmails2 = function(emails){
  const emailFilter = function(str){
    let index = str.search(/@/);
    let s = str.substring(0,index);
    let s2 = str.substring(index+1,str.length);
    let res = '';
    for(let i = 0; i < s.length; i++){
      if(s[i] === '+') break;
      if(s[i] === '.') continue;
      res = res+s[i];
    }
    return res+s2;
  }

  let arr = [];
  for(let i = 0; i < emails.length; i++){
    let t = emailFilter(emails[i]);
    if(arr.indexOf(t) === -1){
      arr.push(t);
    }
  }
  return arr.length;
};

const numUniqueEmails = function(emails){
  let arr = emails.map(str=>{
    let index = str.search(/@/);
    let s = str.substring(0,index);
    let s2 = str.substring(index+1,str.length);
    let res = '';
    for(let i = 0; i < s.length; i++){
      if(s[i] === '+') break;
      if(s[i] === '.') continue;
      res = res+s[i];
    }
    return res+s2;
  });
  let set = new Set(arr);
  return set.size;
}