'undefined'出现在警报中

Question

我使用Javascript来验证一些代码,并且它工作正常,但每当我调用alert来显示错误时,在警报消息的开头我得到'undefined'.因此,当我希望警报显示"请输入低目标"时,我得到'未定义请输入低目标'.有人能告诉我我的代码有什么问题吗？

//validation
        var lowTarget;
        var highTarget;
        var errorList;
        var isValid = true;

        lowTarget = $('input[name="txtLowTarget"]').val();
        highTarget = $('input[name="txtHighTarget"]').val();

        if (lowTarget == "") {
            errorList += "Please enter a Low Target\n";
            isValid = false;
        }
        else {
            if (isNumeric(lowTarget) == false) {
                errorList += "Low Target must be numeric\n";
                isValid = false;
            }
        }

        if (highTarget == "") {
            errorList += "Please enter a High Target\n";
            isValid = false;
        }
        else {
            if (isNumeric(highTarget) == false) {
                errorList += "High Target must be numeric\n";
                isValid = false;
            }
        }

        if (isValid == true) {
            if (!(parseFloat(highTarget) > parseFloat(lowTarget))) {
                errorList += "High Target must be higher than Low Target\n";
                isValid = false;
            }
        }

        if (isValid == false) {
            alert(errorList);
        }

Answer 1

指定一些默认值errorList,例如空字符串

var errorList = "";

直到你这样做,初始值errorList是undefined.