javaScript reserved keywords

Question

I am wondering how JavaScript's reserved keywords / functions are managed.

Example:

According to:

http://www.quackit.com/javascript/javascript_reserved_words.cfm

delete is a reserved keyword by JavaScript.

Then consider the following snippet for some context:

var cookieManager = {
    get: function (name) { 
        // function contents ...
        console.log("cookieManager.get() called");
        return true;
    },
    set: function (name, value, days) {
        // function contents ...
        console.log("cookieManager.set() called");
        return true;
    },
    delete: function (name) { 
        // function contents ...
        console.log("cookieManager.delete() called");
        return true;
    }
};

This object has a delete property, yet the name of it is reserved by JavaScript so it should fail, right?

Yet when I execute cookieManager.delete(); in the webconsole of FireFox I get the following output, suggesting that it works fine:

[11:26:00.654] cookieManager.delete();
[11:26:00.656] cookieManager.delete() called
[11:26:00.657] true

If, however, you run the code in JsLint it says

Problem at line 12 character 5: Expected an identifier and instead saw 'delete' (a reserved word).

delete: function (name) { 

Suggesting that this is a big no no approach and should be avoided.

So when should I take reserved keywords into consideration, as in this example it seems to work just like I want it to ( the delete keyword is in the context of the object cookieManager and thus causes no conflicts, hence it can be used ) or should I abide to the bible that is JsLint and rename anything that is a reserved keyword by javascript? In this context I could easily rename .delete() to .remove().

Haley

Answer 1

Actually this is allowed as per ECMAScript specification. The production rules (Section 11.1.5) for an object literal are:

ObjectLiteral :
    {}
    {PropertyNameAndValueList}
    {PropertyNameAndValueList  ,}

PropertyNameAndValueList :
    PropertyAssignment
    PropertyNameAndValueList , PropertyAssignment

PropertyAssignment :
    PropertyName : AssignmentExpression
    get PropertyName ( ){FunctionBody}
    set PropertyName (PropertySetParameterList){FunctionBody}

PropertyName :
    IdentifierName
    StringLiteral
    NumericLiteral

In your case, you use an IdentifierName as property name. Section 7.6.1 says:

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

Note the difference: You cannot use a reserved keyword as Identifier, but as it is a valid IdentifierName you can use it as PropertyName.

---

Nevertheless, other (versions of) browsers might not tolerate this, so to be on the safe side, I would rename it.

Apart from possible problems with browsers, it might also confuse others who read your code and are not familiar with this rule.

---

FWIW, of course you can always use reserved keywords as strings:

var a = {'delete': 'foo'};
alert(a['delete']);

Survance

So, to clarify, because the production rule for PropertyName uses IdentifierName and not Identifier, it's fine to use delete and so on as a PropertyName? – Decorate

@Delan: I'd say yes. But that does not mean that browsers follow the same rule. – Survance

Also if you run the code in "strict mode" it should throw an error – Delvecchio

Wow +1 for new thing for me :) – Touslesmois

Accepted. Thanks for the updates to your answer as well, they provided some useful information : ) – Haley