如何在jquery中检查null值而不会出现错误？ [英] How can I check a value for null in jquery without getting an error?

问题描述

我有这个代码：

I've got this code:

if (returneddata.daterangeparams.TimeUnitsFrom != null) {

...当值确实为null时抛出此错误（如Chrome开发工具控制台中所示）：



索引：1031未捕获TypeError：无法读取属性'TimeUnitsFrom 'null



那么如何以一种可以避免错误的方式检查null？



根据http://stackoverflow.com/questions/12271750/how-to-check-if-a-variable-is-both-null-and-or-undefined-in-javascript的建议，我甚至尝试过这个：

...which throws this error (as seen in the Chrome Dev Tools console) when the value is, indeed, null:

Index:1031 Uncaught TypeError: Cannot read property 'TimeUnitsFrom' of null

So how can I check for null in a way that I can avoid the error?

Based on a suggestion here http://stackoverflow.com/questions/12271750/how-to-check-if-a-variable-is-both-null-and-or-undefined-in-javascript, I even tried this:

if (returneddata.daterangeparams.TimeUnitsFrom != null && variable !== undefined) {

...但我仍然得到sa我从浏览器的内心发出的声音。



代码在更大的背景下：

...but I still get the same whinging from the guts of the browser.

Code in greater context:

function populatedaterangeprams(rptval, returneddata) {
                    var fromval = '';
                    var toval = '';
                    if (returneddata.daterangeparams.TimeUnitsFrom != null && 

returneddata.daterangeparams.TimeUnitsFrom !== undefined) {
                        fromval = returneddata.daterangeparams.TimeUnitsFrom;
                    }
                    if (returneddata.daterangeparams.TimeUnitsTo != null && 

returneddata.daterangeparams.TimeUnitsTo !== undefined) {
                        toval = returneddata.daterangeparams.TimeUnitsTo;
                    }

                    if (rptval === 1) {
                        // Produce Usage
                        $("#produsagefrom").val(fromval);
                        $("#produsageto").val(toval);
                    } else if (rptval === 2) {
			. . .

那我怎样才能安全地检查空？



< b>我尝试了什么：



基于此处的建议http://stackoverflow.com/questions/12271750/how-to-check- if-a-variable-are-both-null-and-undefined-in-javascript，我甚至试过这个：

So how can I safely check for null?

What I have tried:

Based on a suggestion here http://stackoverflow.com/questions/12271750/how-to-check-if-a-variable-is-both-null-and-or-undefined-in-javascript, I even tried this:

if (returneddata.daterangeparams.TimeUnitsFrom != null && variable !== undefined) {

...但我仍然从内心得到同样的抱怨浏览器。

...but I still get the same whinging from the guts of the browser.

推荐答案

（ ＃produsagefrom ）。val（fromval）;

("#produsagefrom").val(fromval);

（ ＃produsageto ）VAL（toval）。
} else if （rptval === 2 ）{
。 。 。

("#produsageto").val(toval); } else if (rptval === 2) { . . .

那我怎样才能安全地检查空？



< b>我尝试了什么：



基于此处的建议http://stackoverflow.com/questions/12271750/how-to-check- if-a-variable-are-both-null-and-undefined-in-javascript，我甚至试过这个：

So how can I safely check for null?

What I have tried:

Based on a suggestion here http://stackoverflow.com/questions/12271750/how-to-check-if-a-variable-is-both-null-and-or-undefined-in-javascript, I even tried this:

if (returneddata.daterangeparams.TimeUnitsFrom != null && variable !== undefined) {

...但我仍然从内心得到同样的抱怨浏览器。

...but I still get the same whinging from the guts of the browser.

你需要检查每一步，看看它是否 null ：

You need to check each step to see if it's null:

if (returneddata != null && returneddata.daterangeparams != null && returneddata.daterangeparams.TimeUnitsFrom != null) {

这篇关于如何在jquery中检查null值而不会出现错误？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！