We have an object `subjects`

in the editor.

If we try to add the value `Mathematics`

to the key `104`

using the **dot operator**
it gives an error.

This is because,
the name of the key is not
a proper variable name.
Now, to add the value of this property,
we must use the **bracket notation**.

In the example given above,
we add the value `Mathematics`

to
the `104`

key in the object
using **bracket notation**.