JSFiddle - React, Tailwind, and code Playground

by César Miguel Cação

HTML

<input type="text" id="NumDoc"/>
<input type="button" onclick ="NumDocContrato()" />

JavaScript

NumDocContrato = function (){
    var num = $("#NumDoc").val();
	 var numDigitNum = num.length;
	 var numInt = parseInt(num);
	 var numDigitsNumINT = String(numInt).length;
	 var numZeroAdd = "";
	 if (numDigitNum != numDigitsNumINT) {
		 numDigitNum = (parseInt(numDigitNum) - parseInt(numDigitsNumINT))
		 for (var i = 0; i < numDigitNum; i++)
		 { numZeroAdd += "0"; }
	 }
	 var num = numZeroAdd + (parseInt(num) + 1);
	 alert(num);
	 $("#NumDoc").val(num);
}