Hello, I am kizito, I just started learning javascript, but this code is not running, can someone please explain to why it is not running

<form name= "form1" onSonSumit="return">
    Enter your first number
    <input type ="text" name="nfirstEntry"><br>
    Enter your second Number
    <input type ="text" name="nSecondEntry"><br><br>
    Answer : 
    <input type="text" name="operation" value= "  "> <br>
    <input type=" button" name= "Add" value=" + " onClick="fncall()">
</form>

function fncall()
{
    var nResult;
    var nFirst, nSecond;
    nFirst= parseInt(form1.nFirstEntry.value);
    nSecond=parseInt(form1.nSecondEntry.value);
    nResult = fnAdd(nFirst,nSecond);
    form1.operation.value = nResult;
}

function fnAdd (nFirst,nSecond)
{
    return nFirst+nSecond;
}