JS 通过变量调用对象属性

当我有一个对象并且我想引用其中的一个属性时，我可以使用例如

When I have an object and I want to refer to a property within it, I can use e.g.

objectName.propertyName 

当我有一个子属性"时，我可以使用

and when I have a "subproperty" I can use

objectName.propertyName.propertyName

但是如何使用具有这种语法的变量?

But how can I use a variable with this syntax ?

objectName.myvar.propertyName

显然这是行不通的.该变量被解释为一个字符串本身并要求带键的值:myvar".

Obviously this does not work. The variable is interpreted as a string itself and calls for the value with the key: "myvar".

如何使用此语法声明变量，以便像这样使用:

How do I have to declare the variable using this syntax to be used like this:

var myvar = qwertz; objectName.myvar.propertyName 

并被解释为

var myvar = qwertz; objectName.qwertz.propertyName