如何自动将属性添加到未定义的对象? [英] How to automatically add properties to an object that is undefined?

问题描述

是否有一种简单的方法可以自动将属性添加到对象(如果属性尚不存在)?

Is there an easy way to automatically add properties to objects if they don't already exist?

请考虑以下示例:

var test = {}
test.hello.world = "Hello doesn't exist!"

这不起作用，因为未定义 hello .

This doesn't work because hello isn't defined.

之所以这样问，是因为我有一些不知道它们是否已经存在 hello 的现有对象.实际上，我在代码的不同部分中有很多这些对象.总是检查 hello 是否存在以及是否不创建新对象(如:

The reason why I'm asking this is because I have some existing objects for which I don't know if they allready have hello or not. I actually have a lot of these objects in different parts of my code. It is very annoying to always check if hello exists and if it doesn't create a new object like:

var test = {}
if(test.hello === undefined) test.hello = {}
test.hello.world = "Hello World!"

在此示例中，是否可以自动创建像 hello 这样的对象?

Is there a way to automatically create an object like hello in this example?

我的意思是在php中这样:

I mean something like that in php:

$test = array();  
$test['hello']['world'] = "Hello world";   
var_dump($test);

输出:

array(1) {
  ["hello"] => array(1) {
    ["world"] => string(11) "Hello world"
  }
}

好吧，这是一个数组，但是在js数组中，它与对象的问题相同.

Ok it's an array but in js arrays it is the same problem as with objects.

推荐答案

var test = {};
test.hello = test.hello || {};
test.hello.world = "Hello world!";

如果未定义 test.hello ，则将其设置为空对象.

If test.hello is undefined, it gets set to an empty object.

如果先前已定义 test.hello ，则它保持不变.

If test.hello was previously defined, it stays unchanged.

var test = {
  hello : {
    foobar : "Hello foobar"
  }
};

test.hello = test.hello || {};
test.hello.world = "Hello World";

console.log(test.hello.foobar); // this is still defined;
console.log(test.hello.world); // as is this.

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