Js ile gelen input değerini almak yada değişkene atamak

<script type="text/javascript">


function toplam(){

var motor1 = document.getElementById("motor_id").value;




if(motor1 == "" || motor1 == "" ){

document.getElementById("2").value="boş alan bırakmayınız";

} else {


document.getElementById("motorfiyat").value=parseFloat(motor1) ;




}



}

setInterval("toplam()", 100);



</script>

<select id="motor_id" name="motor_id" class="form-control" required>

<option value="0" >Motor Tip</option>

 

<option value="1">Fiat Motor</option>
<option value="2>Reno Motor</option>
<option value="3">Volvo Motor</option>
 




</select>



<input value="" type="text" id="motorfiyat" name="motorfiyat">

<select id="motor_id" name="motor_id" class="form-control" required>
<option value="<?php echo $motorcek['motor_id'] ?>"> <?php echo $motorcek['motor_ad'] ?> </option>
</select>

<select id="motorfiyat" name="motor_id" class="form-control" required>
<option value="<?php echo $motorcek['motorfiyat'] ?>"> <?php echo $motorcek['motor_ad'] ?> </option>
</select>

<select id="motor_id" name="motor_id" class="form-control" required>
<option value="<?php echo $motorcek['motor_id'] ?>"> <?php echo $motorcek['motor_ad'] ?> </option>
</select>

<select id="motorfiyat" name="motor_id" class="form-control" required>
<option value="<?php echo $motorcek['motorfiyat'] ?>"> <?php echo $motorcek['motor_ad'] ?> </option>
</select>

var motor_id = $("#motor_id").val();
var motorfiyat = $("#motorfiyat").val();

$.ajax({
type: "POST",
url: "islem.php",
data: "motor_id="+motor_id+"&motorfiyat="+motorfiyat,
success: function(cevap){

alert(cevap);

}
});