var result = "";什么意思？

var result = "";

        switch(oSlt) {
        case "+":
            result = parseFloat(oTxt1) + parseFloat(oTxt2);
            break;
        case "-":
            result = parseFloat(oTxt1) - parseFloat(oTxt2);
            break;
        case "*":
            result = parseFloat(oTxt1) * parseFloat(oTxt2);
            break;
        default:
            result = parseFloat(oTxt1) / parseFloat(oTxt2);
    }
    document.getElementById("fruit").value = result;