How is "first-name" a reserved word in JavaScript?

Question

Note: This question pertains to the book 'JavaScript: The Good Parts' written by Doug Crockford. As I was reading a chapter on Objects, I came across a statement as follows:

The quotes around a property's name in an object literal are optional if the name would be a legal JavaScript name and not a reserved word. So quotes are required around "first-name", but are optional around "first_name".

And the following is the example of an object literal provided in the book:

var stooge = {
    "first-name": "Jerome",
    "last-name": "Howard"
};

Now, I might have misinterpreted the text here but to me it seems like Mr. Crockford is saying first-name (with the hyphen) IS a reserved word whereas first_name (with the underscore) is not. If that is the case, I don't understand how the former can be a reserved word. I found no other explanation in the book why this is. Can someone please explain?

Calica

Answer 1

It is not a reserved word. Without the quotes, javascript will interpret the - character as a subtraction operator, attempt to perform the operation, and fail.

One reason for this is that javascript prefers to ignore whitespace whenever it can. Thus 2 - 3 is the same as 2-3.

Putting the whole thing in quotes causes the js to interpret as just another character, not an operator.

Predilection

Jeffman, it makes perfect sense. It didn't occur to me first how the hyphen can be interpreted as such! – Calica