为什么按“=”结果不显示出来呢

 function count(){
    var oTxt1 = document.getElementById("txt1").value;
    var oTxt2 = document.getElementById("txt2").value;
    var oSlt = document.getElementById("select").value;
    var result = " ";
    switch(oSlt) {
        case "+":
            result = parseInt(oTxt1) +parseInt(oTxt2);
            break;
        case "-":
            result = parseInt(oTxt1) - parseInt(oTxt2);
            break;
        case "*":
            result = parseInt(oTxt1) * parseInt(oTxt2);
            break;
        default:
            result =parseInt(oTxt1) / parseInt(oTxt2);
    }
    document.getElementById("fruit").value =  result;
    
   }