JSFiddle - React, Tailwind, and code Playground

HTML

<select id="area">
    <option value='1001'>Mong kok</option>
    <option value='1002'>Wan Chai</option>
    <option value='1003'>Sai Kung</option>
</select>
<input id='address' type='text' />

JavaScript

var area = {
    'Mongkok': 1001,
    'Wan Chai': 1002,
    'Sai Kung': 1003
};

$("#address").keyup(function() {
    var adress = $(this).val();
    for (var v in area) {
        if (adress.indexOf(v) >= 0) {
            $("#area").val(area[v]);
            break;
        }
    }
});