Quick script to get SharePoint user properties (LoginName, Title, Email) for multiple users, via the Chrome console, using async/await, Promise.all, fetch, computed properties and rest parameters.

GetUsers.js

(async function() {
    let userIds = [239, 405];

    // computed property name: [prop]:
    // rest parameters: ...props
    // stolen from: https://stackoverflow.com/a/25554551
    function pick(o, ...props) {
        return Object.assign({}, ...props.map(prop => ({[prop]: o[prop]})));
    }

    async function getUser(userId) {
        let apiUrl = `${_spPageContextInfo.webAbsoluteUrl}/_api/web/GetUserById(${userId})`;

        let options = {
            method: "GET",
            headers: {
                "Accept": "application/json; odata=verbose"
            },
            credentials: "include"
        };
        
        let response = await fetch(apiUrl, options);
        
        if(response.ok) {
            let item = await response.json();            
            return pick(item.d, "LoginName", "Title", "Email");
        }
        else {
            return Promise.reject(new Error(`${response.status}: ${response.statusText}`));
        }
    }

    let results = await Promise.all(userIds.map(getUser));
    console.table(results);
})();