Still confused about JavaScript Expressions and Statements

Question

I found this PDF here and in it the author describes an expression as any valid set of literals, variables, operators, function calls and expressions that evaluate to a single value i.e.

3 + 7
3 + 7 + 10 + ""
"Dr." + " " + "Pepper"

That all seems fine to me. An a statement is any set of declarations, method and function calls and expressions that performs some action i.e.

var num = 1
document.write("hello")

But later on they refer to the last line of the examples below as statements

var salutation = "Greetings, "
var recipient = "Earthlings"
salutation + recipient //statement

var greeting = "Greetings, "
greeting += "Earthlings" //statement

Why isn't salutation + recipient and greeting += "Earthlings" considered an expression when they are adding two strings like in their expression example "Dr." + " " + "Pepper"

Many thanks

Justin Niessner · Accepted Answer · 2010-06-21 12:08:59Z

1

Because a statement can contain expressions.

A statement is any set of declarations, method and function calls and expressions that performs some action

answered Jun 21, 2010 at 12:08

Justin Niessner

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2 Comments

screenm0nkey Over a year ago

@ Justin - Thanks for the response. I understand that a statement can contain expressions by why is salutation + recipient a statement and "Dr." + "Pepper" an expression? They are both adding strings together.

S.Lott Over a year ago

@Nick Lowman: An Expression IS a Statement. An Expression is one kind of Statement. They aren't exclusive categories.

Paolo · Accepted Answer · 2010-06-21 12:09:41Z

1

I think the first is a mistake, I suspect the author mean to type += instead of just +. The second is a statement because it's shorthand for

greeting = greeting + "Earthlings"

and you are assigning the result of the string concatenation (an expression) back to the original variable (which makes it a statement).

answered Jun 21, 2010 at 12:09

Paolo

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