JSFiddle - React, Tailwind, and code Playground

HTML

<form>
Number to words<BR>
<BR>Number/N&uacute;mero 
    <INPUT NAME="Number" TYPE="text" SIZE="60" value="2,658.12"/> <BR><TEXTAREA NAME="Spanish" ROWS="5" COLS="90"></TEXTAREA><BR>
</form>

JavaScript

$(function() {
    $('input[name=Number]').on('keyup change blur',function() {
        Calculate( this.form );
    });
    Calculate( $('form')[0] );
});


function FixSpaces(s){
//returns a string with no double spaces inside
	var t='';
	for(var i=0; i<s.length; i++){
		if (i>0){
			if (!((s.substring(i-1,i)==' ')&(s.substring(i,i+1)==' ')))
				t=t+s.substring(i,i+1);
		}else
			t=t+s.substring(i,i+1);
	}
	return t;
}

function Calculate(form)  {
//fill forms with text
	var Ner = form.Number.value; 
	form.Spanish.value = NumerosPalabras(Ner);
 
}

function REPLICATE(n, c){
//returns n times char c
	var t='';
	for(var i=1; i<=n; i++)
		t=t+c;
	return t;
}

function NumerosPalabras(s)  {
//Spanish words for numbers
    s = s.replace(',','');
	var a,b,c,j,orlen,result=' ',
        cents = s.split('.')[1] || '00',
        s = s.split('.')[0] || s;
	if (s=='0') {return ('CERO');}
		orlen=s.length;
	if ((s.length % 3)>0)
		s=' '+s;
	if ((s.length % 3)>0)
		s=' '+s;
	for (var i = 0; i < s.length; i=i+3) {
		j=s.length-i-1;
		a=s.substring(j, j+1);
		b=s.substring(j-1, j);
		c=s.substring(j-2, j-1);
		if (a!=' '){ 
			if ((i==3)&(c+b+a!=',000') ) {result='MIL '+result;}
			else if (((i==6)&(c+b+a!=',000') ) &(orlen==7)&(a=='1')) {result='MILLÓN '+result;}
			else if ((i==6)&(c+b+a!=',000') ) {result='MILLONES '+result;}
			else if ((i==9)&(c+b+a!=',000') ) {result='MIL MILLONES '+result;}
		}
		if ((b!=1) | (b==' ')){
			if (a==1){result='UNO '+result;}
			else if (a==2){result='DOS '+result;}
			else if (a==3){result='TRES '+result;}
			else if (a==4){result='CUATRO '+result;}
			else if (a==5){result='CINCO '+result;}
			else if (a==6){result='SEIS '+result;}
			else if (a==7){result='SIETE '+result;}
			else if (a==8){result='OCHO '+result;}
			else if (a==9){result='NUEVE '+result;}
		}
		if ((b!=' ')&(b!=',0')){
			if ((b==1) | (b==2)){
				if (b+a==10){result='DIEZ '+result;}
				else if (b+a==11){result='ONCE '+result;}
				else if (b+a==12){result='DOCE...