How can I statically declare a Javascript object instance (a.k.a "associative array") whose property names (a.k.a keys) contain dashes?

Question

I want to statically declare a Javascript object (sometimes referred to as "associative array" when used as such) whose property names ("keys") contain dashes?

Without dashes (works):

myObject = {field_1:"aaa", field_2:"bbb"};

With dashes (results in syntax error):

myObject = {field-1:"aaa", field-2:"bbb"};

(And yes, I'm fully aware that such properties containing dashes can only be referenced by using "bracket notation" rather than "dot notation", but that's a completely other story, I'm only talking about the case of static declaration of such objects here.)

FYI, it's called *bracket notation* and *dot notation* (the notation has nothing to do with arrays). And no, this is actually closer related than you think. You have to use bracket notation + a string literal if the property name is not a valid identifier name. Similarly for object literals, you have to use a string literal if the property name is not valid identifier name. Same reason, same solution. — Felix Kling, Nov 05 '16 at 01:48

0.sh · Accepted Answer · 2016-11-05T12:50:54.680

3

you have to wrap the property names in quote to read "field-1" as a string.

var myObject = {"field-1":"aaa", "field-2":"bbb"}
console.log(myObject["field-1"], myObject["field-2"])

//computed properties
var name1 = "field-1"
var name2 = "field-2"

var myObject = {
     [name1]: "aaa",
     [name2]: "bbb"
}

console.log(myObject["field-1"], myObject["field-2"])

edited Nov 05 '16 at 12:50

answered Nov 05 '16 at 01:39

0.sh

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2

Please elaborate on why. – Felix Kling Nov 05 '16 at 01:45
Excellent, thanks! (please change "bbbb" to "bbb" in the "computed properties" example code though, for consistency and to avoid unnecessary confusion) – QuestionOverflow Nov 05 '16 at 02:45

Felix Kling · Answer 2 · 2016-11-05T02:51:15.777

Inside an object literal, property names can be defined in four ways:

as an identifier name (foo)
as a number literal (42)
as a string literal ('foo bar')
as a computed property ([foo + 'bar'])

field-1 is neither of those. It's not an identifier because the character - is not valid in identifier names. It's relatively easy to know whether something is a valid identifier name: If it's not a keyword and not a valid variable name, it's not a valid identifier name. That is, since it's invalid to declare the variable

var field-1 = 42;

you cannot use it in a object literal either.

You have to use a string literal instead. A string literal can contain any character sequence:

myObject = {'field-1':"aaa"};

How can I statically declare a Javascript object instance (a.k.a "associative array") whose property names (a.k.a keys) contain dashes?

2 Answers2