javascript - 如何忽略 jQuery 中的两个 null 或未分配的值？

Question

我有这段代码来比较两个值以验证它们是否相同:

$(document).on("blur", "[id$=boxSection5Total]", function (e) {
    var totalvalue = $(this).val();
    var paymenttotalvalue = $('[id$=boxPaymentAmount]').val();
    if (totalvalue != paymenttotalvalue) {
        console.log("The value in 'Total' does not equal the previous value in 'Payment Total.'");
        alert("The value in 'Total' does NOT equal the previous value in 'Payment Total.' payment total is " + paymenttotalvalue + " and total is " + totalvalue);
    }
    else {
        console.log("The value in 'Total' DOES equal the previous value in 'Payment Total'");
    }
});

但是，如果两个文本元素都留空，则会失败 - 它们被认为不相等(“if (totalvalue != paymenttotalvalue)”条件为 true)。

如何重构代码，使其忽略两个元素都留空的情况？

类似于:

$(document).on("blur", "[id$=boxSection5Total]", function (e) {
    var totalvalue = $(this).val();
    var paymenttotalvalue = $('[id$=boxPaymentAmount]').val();
    if ((totalvalue == null) & (paymenttotalvalue == null)) {
        return;
    }
    . . .
});

？

“boxSection5Total”和“boxPaymentAmount”都是文本元素(文本框)。

Answer 1

如果您想专门检查 null，您应该尝试这样的操作。

if (totalvalue !== null && paymenttotalvalue !== null && totalvalue != paymenttotalvalue)

如果您想检查是否不真实(另请参阅此处:JavaScript: how to test if a variable is not NULL)，您可以使用以下内容:

if (totalvalue && paymenttotalvalue && totalvalue != paymenttotalvalue)