Do reserved words need to be quoted when set as property names of JavaScript objects?

Question

Given an object literal, or `jQuery(html, attributes)` object, does any specification state that reserved words, or future reserved words MUST be quoted? Or, can, for example, `class` be set as a property name of an object without using quotes to surround the property name, without the practice being contrary to a specification concerning identifiers, property names, or use of reserved words? Seeking a conclusive answer as to this question to avoid confusion. ``` let objLit = { class: 123, var: "abc", let: 456, const: "def", import: 789 } console.dir(objLit); jQuery("

012

", { class: "ghi" }) .appendTo("body"); ``` ``` ``` Related: What is the difference between object keys with quotes and without quotes? Comments on this answer Specification - 7.6 Identifier Names and Identifiers: Identifier Names are tokens that are interpreted according to the grammar given in the “Identifiers” sectio…

Accepted Answer

ECMAScript 5+

No, quotes were not needed since ECMAScript 5. Here's why:

As mentioned in your post, from the ECMAScript® 5.1 Language Specification:

7.6 Identifier Names and Identifiers

Identifier Names are tokens that are interpreted according to the grammar given in the “Identifiers” section of chapter 5 of the Unicode standard, with some small modifications. An `Identifier` is an `IdentifierName` that is not a `ReservedWord` (see 7.6.1).

[...]

Syntax

```
Identifier ::
  IdentifierName but not ReservedWord
```

By specification, a `ReservedWord` is:

7.6.1 Reserved Words

A reserved word is an `IdentifierName` that cannot be used as an `Identifier`.

Syntax

```
ReservedWord :: 
  Keyword
  FutureReservedWord
  NullLiteral
  BooleanLiteral
```

This includes keywords, future keywords, `null`, and boolean literals. The full list is as follows:

7.6.1.1 Keywords

```
break    do       instanceof typeof
case     else     new        var
catch    finally  return     void
continue for      switch     while
debugger function this       with
default  if       throw 
delete   in       try   
```

7.6.1.2 Future Reserved Words

```
class enum   extends super
const export import
```

7.8.1 Null Literals

```
null
```

7.8.2 Boolean Literals

```
true
false
```

The above (Section 7.6) implies that `IdentifierName`s can be `ReservedWord`s, and from the specification for object initializers:

11.1.5 Object Initialiser

[...]

Syntax

```
ObjectLiteral :
  { }
  { PropertyNameAndValueList }
  { PropertyNameAndValueList , }
```

Where `PropertyName` is, by specification:

```
PropertyName :
  IdentifierName
  StringLiteral
  NumericLiteral
```

As you can see, a `PropertyName` may be an `IdentifierName`, thus allowing `ReservedWord`s to be `PropertyName`s. That conclusively tells us that, by specification, it is allowed to have `ReservedWord`s such as `class` and `var` as `PropertyName`s unquoted just like string literals or numeric literals.

ECMAScript <5

To go more in depth as to why this wasn't allowed in previous versions before ES5, you have to look at how `PropertyName` was defined. Per the ECMAScript® 3 Language Specification:

```
PropertyName :
  Identifier
  StringLiteral
  NumericLiteral
```

As you can see, `PropertyName` was an `Identifer` - not an `IdentifierName`, thus leading to the inability for `ReservedWord`s as `PropertyName`s.

Do reserved words need to be quoted when set as property names of JavaScript objects?

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