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;
};