key of a JavaScript object must be a string

Question

In JavaScript, if you type

typeof("2")

you should get string.

And if you type

typeof(2)

you should get number.

Now my question is, it is said that when you define an object, the key must be a string.

so this is legal

apple = {"color":"red"}

However, if I change the key to a number wrapped in the inverted commas, it should work as anything inside of inverted commas

apple={"2": "red"}

But If I call the object property, apple.2, this will fail with error Unexpected number.

so am just curious, what am I missing here while defining the objects in JavaScript.

FYI typeof is an operator, not a function, so the parentheses are unnecessary. The object's key must be a string, so you'd need to access it via apple["2"], not using a number via apple.2. — Heretic Monkey
– Heretic Monkey, Commented May 21, 2021 at 19:11
Dot notation is restricted to valid JS identifiers, 2 is not a valid JS identifier. — Dave Newton
– Dave Newton, Commented May 21, 2021 at 19:16

Steve Bunting · Accepted Answer · 2021-05-21 19:31:47Z

3

An object key must be a string, but JavaScript allows you to assign an object with a number. It's just converted to a string behind the scenes, so:

apple = {2: "red"}

is the same as:

apple = {"2": "red"}

Using dot notation requires a valid identifier. So you can not access the property with apple.2 as 2 is a number, instead, you have to use bracket notation, either apple["2"] or apple[2].

Incidentally, there are other cases which can not be accessed with dot notation, such as:

apple = {"hyphenated-key": true}

Trying to access apple.hyphenated-key would not work, you have to use bracket notation as such apple["hyphenated-key"].

answered May 21, 2021 at 19:31

Steve Bunting

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1 Comment

saran Over a year ago

and after some research, we can't do foo.bar.baz for an object which is defined like foo={bar.baz : value}. I think objects as associative arrays make more sense in most of the little complicated-shaped objects. If anyone wants to unnderstand better, follow the link

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