Javascript检查对象属性是否存在，即使对象未定义 [英] Javascript check if object property exists, even when object is undefined

问题描述

我想检查一个对象是否存在，并且有一个属性。目前我收到一个myObject is undefined错误，它会停止检查。

I want to check if an object exists, and has a property. Currently I get a "myObject is undefined" error that stops the check.

即使myObject可能不存在，如何使以下内容仍能正常工作？

How can I make the following still work correctly even when myObject may not exist?

if (myObject.myProperty) {
  ...
} else {
  ...
}

我试图甚至检查对象/变量是否存在但是收到错误：

I am trying to just even check if a object / variable exists but getting an error:

if（foo）{console.log（'hello'）; } 给出错误Uncaught ReferenceError：foo未定义。这是一个jsfiddle http://jsfiddle.net/cfUss/

if (foo) { console.log('hello'); } gives the error Uncaught ReferenceError: foo is not defined. Here is a jsfiddle http://jsfiddle.net/cfUss/

推荐答案

您可以使用短路&& 运营商：

You can use the "short circuit" && operator:

if (myObject && myObject.myProperty) { 
    ...
}

如果 myObject 为falsey（例如未定义）& ;& 运算符不会试图评估右手表达式，从而避免尝试引用不存在的对象的属性。

If myObject is "falsey" (e.g. undefined) the && operator won't bother trying to evaluate the right-hand expression, thereby avoiding the attempt to reference a property of a non-existent object.

变量 myObject 必须已经声明了，上面的测试是针对是否已经分配了一个价值。

The variable myObject must have course already have been declared, the test above is for whether it has been assigned a defined value.

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