Allow reserved words for properties?

[Ian Bicking]

Under Objects it says you shouldn't use reserved words. I'm not sure this is important, though avoiding them might make sense for readability. At least using klass instead of class would seem wrong to me, as you are corrupting a word instead of finding a readable synonym (like type).

Right now you can use just about anything. E.g., test = {function: 1}; test.function === 1 –but additionally I think we can be confident this will continue to be the case. IndexedDB uses the method cursor.continue() which isn't just a future-protected reserved word (like class) but a reserved word right now. But IndexedDB represents current API design by people involved in the standardization process.

I think it's questionable from a readability point of view to use current keywords, but I don't see any reason at all to avoid words reserved for possible future use (class and private, as used in the example, are both examples of that).

[Harrison Shoff]

True.

This was one of those Airbnb specific things. We support IE8 and IE8 doesn't support reserved words as property names ([source](http://kangax.github.com/es5-compat-table/#Reserved words as property names)):

var obj = {
  class: function(){}
};

// doesn't work in IE8
obj.class();

You can use them in IE8 if you use the subscript notation:

// this works
obj['class']();

but this contradicts our style guide preference of using dot notation to access properties by name and subscript notation to access properties by variable #properties.

This is another one of those preference decisions where it might sound like "you can't use reserved words as property names" but really what we're trying to say is "we would prefer if you didn't...for now".

Maybe it would be helpful to note what the reserved and future reserved words are and explain that they can be used as Identifiers but not as an IdentifierName ES5 #7.6.1 in [supporting browsers](http://kangax.github.com/es5-compat-table/#Reserved words as property names).

// SyntaxError: unexpected reserved word
function class(){}

[jack]

This is also not supported in IE7, such as
var obj = {
default: 'this is default key',
private: 'OK',
class: 'this is class key'
};
The "default" and "class" key here does not work in IE7/IE8, but not for the "private" key

[Timo Tijhof]

Note that this isn't an "IE bug". It's not supported in old IE because IE's JScript engine correctly follows the ECMAScript 3 specification in this regard; which explicitly defines PropertyName as an Identifier, which is "an IdentifierName that is not a ReservedWord".

This was not by design, but at the time merely to document the status quo of different browsers and to ensure consistency. Other browser's engines had this behaviour as well.

Since property names leave no ambiguity with other operators, this useless restriction was removed in ES5 where PropertyName has been redefined as a plain IdentifierName (https://es5.github.io/#x11.1.5). ES5 is still relatively new (not unlike CSS3 and HTML5) and first implemented in IE10 (almost in IE9), Firefox 4, Safari 6 and Chrome 19.

I'd recommend using something like JSHint (and set option es3: true), and also use it in your editor, to automatically catch these (and other things) ahead of time.

[Rico Sta. Cruz]

considering most people use Babel.js now (does Airbnb?), maybe this can be rescinded. It will automatically transpile aoeu.class to aoeu['class']

[Josh Perez]

Yeah this can be updated.