JSFiddle - React, Tailwind, and code Playground

by IllusionMH

HTML

<select id="sel1">
     <option value="1">111</option> 
     <option value="2">222</option> 
     <option value="3">333</option> 
     <option value="4">444</option> 
</select>
<input type="text" id="inp1" />
<input type="text" id="inp2" />

JavaScript

document.getElementById("sel1").onchange = function() {
    document.getElementById("inp1").value = this.value;
    document.getElementById("inp2").value = this.options[this.options.selectedIndex].text;
};

document.getElementById("inp1").onchange = function() {
    var sel = document.getElementById("sel1"),
        i, n;
    for (i = 0, n = sel.options.length; i < n; i += 1) {
        if (this.value === sel.options[i].value) {
            sel.options.selectedIndex = i;
            document.getElementById("inp2").value = sel.options[i].text;
            break;
        }
    }
};