如何检查对象中是否存在对象 [英] How to check if object within object exists

问题描述

似乎以下用于检查对象成员是否存在的技术会产生错误，因为在检查之前尚未声明'bar'父对象，这意味着我必须在检查之前声明它或使用两个'typeof'表达式，其中任何一个都是超额代码：

It seems that the following technique for checking the existence of an object member produces an error because the 'bar' parent object hasn't been declared before the check, which means I either have to declare it before the check or use two 'typeof' expressions, either of which would be excess code:

var foo = {},
    newVal = (typeof foo.bar.myVal !== 'undefined' ? foo.bar.myVal : null );

Error: foo.bar is undefined

那么，你如何检查如果未声明的对象中的成员存在而没有产生错误？

So, how do you check if a member within an undeclared object exists without producing an error?

我喜欢javascript，但有时......

I love javascript, but sometimes...

推荐答案

只需使用以下代码即可：

It can be done simply using the code below:

var newVal = (foo && foo.bar && typeof foo.bar.myVal !== 'undefined') ? foo.bar.myVal : foo.bar.myVal

属性为null或未定义，它将是评估为false，因此上述代码只会处理第一个'false'语句。

A property is null or undefined, it will be evaluated as false so the above code will only process up to the first 'false' statement.

这篇关于如何检查对象中是否存在对象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！