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;
2017-03-11
聲明一個變量，并且變量值為null。