[Dilettante_Pro]

Возвращаясь к самому началу темы....

<div>
   Период <select id="period">
   <option value = "25">25</option>
   <option value = "20">20</option>
   <option value = "15">15</option>
   <option value = "10">10</option>
</select>
<br>
Сумма депозита <input type="text"  id="deposit" class = "onlyDigits"  value="10"/><br>
<input type="button" onclick="summ();" value="Расчет" >
</div>
<div id="debet" ></div>
<div id="summa"></div>

<script>
var debet= [{percent: 2, period: 25, min: 10, max:500},{percent: 3.3, period: 20, min: 510, max:5000},{percent: 4.5, period: 15, min: 5010, max:10000},{percent: 6.3, period: 10, min: 10010, max:100000}],
      minDebet = 10,
      maxDebet = 500,
      percent = 2;
 
function onlyDigits() {
          this.value = this.value.replace(/[^\d]/g, "");
         document.querySelector("#debet").innerHTML = " ";
         document.querySelector("#summa").innerHTML = ""; 
}
document.querySelector(".onlyDigits").oninput = onlyDigits;
function summ() {
          var dep = document.querySelector('#deposit'),
                depv = +dep.value;
          if(depv < minDebet) dep.value = minDebet.toString();
          if(depv > maxDebet) dep.value = maxDebet.toString();
          depv = +dep.value;
         var period = document.querySelector("#period").value;
         var result = (depv * percent * period / 100);
         document.querySelector("#debet").innerHTML = "Доход: " + result;
         document.querySelector("#summa").innerHTML = "Итого: " + (result + depv);
}
document.querySelector("#period").onchange = function() {
     var period = +this.value;
     for(var i = 0; i < debet.length; i++) {
         if(debet[i].period == period) {
            minDebet = debet[i].min;
            maxDebet = debet[i].max;
            percent = debet[i].percent;
            document.querySelector("#deposit").value = minDebet.toString();
         document.querySelector("#debet").innerHTML = " ";
         document.querySelector("#summa").innerHTML = ""; 
        }
     }
}
</script>