在Javascript中检查一下isEmpty？ [英] Checking something isEmpty in Javascript?

问题描述

如何在Javascript中检查变量是否为空？抱歉这个愚蠢的问题，但我是Javascript的新手！

How can I check if a variable is empty in Javascript? Sorry for the stupid question, but I'm a newbie in Javascript!

if(response.photo) is empty {
    do something
else {
    do something else
}

response.photo 来自JSON，有时可能为空，空数据单元格！我想检查它是否为空。

response.photo was from JSON, and it could be empty sometimes, empty data cells! I want to check if it's empty.

推荐答案

如果您正在测试一个空字符串：

If you're testing for an empty string:

if(myVar === ''){ // do stuff };

如果您正在检查已声明但未定义的变量：

If you're checking for a variable that has been declared, but not defined:

if(myVar === null){ // do stuff };

如果您正在检查可能未定义的变量：

If you're checking for a variable that may not be defined:

if(myVar === undefined){ // do stuff };

如果您同时检查两个ie，则变量为null或未定义：

If you're checking both i.e, either variable is null or undefined:

if(myVar == null){ // do stuff };

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