JSFiddle - React, Tailwind, and code Playground

HTML

<input type="month" id="incidentDate" name="incidentDate" class="incidentDate" />

<input type="text" id="incidentMonth" value="2011">
    <input type="text" id="incidentYear" value="5">

JavaScript

var y= $("#incidentMonth").val() + "-" + $("#incidentYear").val();
var x= new Date(y);
var m=x.getFullYear().toString() +'-'+ (parseInt(x.getMonth())+1).toString()

m= m.split('-')[1].length<2? m.split('-')[0]+'-0'+m.split('-')[1]:m.split('-')[0]+'-'+m.split('-')[1]
document.getElementById("incidentDate").value = m;