JSFiddle - React, Tailwind, and code Playground

HTML

Email ID: <input type="text" id="autocomplete" />

JavaScript

$(document).ready(function() {
    var autocompOpts = {
        minChars:0,
        matchSubset:false,
        matchContains: true,
        source : []
    };

    var domains = [
        "@gmail.com",
        "@yahoo-inc.com",
        "@yahoo.com",
        "@yahoo.co.in",
        "@rediff.com",
        "@rediffmail.com",
        "@hotmail.com",
        "@msn.com"
    ];

    var input = $("#autocomplete");
    input.autocomplete(autocompOpts);

    input.bind('keyup', function(event) {
        if (event.shiftKey == 1 && event.keyCode == 50) {
            var userName = $(this).val();
            userName = userName.substring(0, userName.length - 1);
            $.each(domains, function(index,domain){
                autocompOpts.source.push(userName + domain);
            });
            $(this).autocomplete(autocompOpts);
        }
    });
});