_ (underscore) is a valid
variable name in JavaScript.
It should only be used
to indicate that a parameter
is not being used in a function.
Consider the following example:
In the example given above,
the function passed as the argument to forEach
has two parameters - fruit and index.
But the function does not use
the fruit parameter
and
we should not have any unused variables.
Since the function uses positional parameters,
the index can only be accessed in the second parameter.
So we can use _ as the first parameter
in order to omit the first parameter
and
have index as the second parameter,
as shown in the example below:
The parameter name _ can be used
to indicate that the parameter
will not be used in the function.