Dynamic Access
Get to know how to access members dynamically.
We'll cover the following
To access a field, a property, or a method, we use the dot notation in JavaScript much like in languages like Java, C#, and many other languages. However, we can also access a member of an instance using the []
operator; we’ll look at yet another alternative to this in Getting and Setting Properties.
Accessing instance members
Following are the rules to access instance members:
- Use the dot notation, like
sam.age
orsam.play()
, if you know the member name at code writing time. - If the member name is not known until runtime, use the
[]
notation.
Suppose variables named fieldName
and methodName
contain the name of a field and a method—for example, "age"
and "play"
, respectively. Then, sam[fieldName]
is equivalent to writing sam.age
and sam[methodName]()
is like writing sam.play()
.
If you’re curious to find all the members in an instance named
instance
, use theObject.keys(instance)
method. This method is called keys because JavaScript considers objects to be like hashmaps, with keys and values.
Alternatively, you can iterate over the members using the for member in instance {}
form.
Example
Let’s try out these facilities with an example.
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