Trailing commas in Object/Array literal

[trantorLiu]

Are trailing commas good style in javascript?
I always use them for convenience.

var tom = {
  name: 'Tom',
  age: 20,
  friends: [
    'Jerry',
  ],
};

[op1ekun]

Just watch out for IE browsers. If your last element is followed by coma IE will expect another element there (probably will whine about expecting object). Was a bit of hell back in the days of IE6...

It will give you trouble mostly ;) in IE6/IE7.

UPDATE: Of course I don't recommend it! Sorry for any confusion :)

[serbanghita]

IE7 throws error, also beware that IE9 in quirks mode (imagine a website that has no DOCTYPE) will throw the same error. I would not recommend this.

[hshoff]

I would not recommend it as well. It has the potential to cause more trouble than the benefit it gives you.
Some implementations would actually add length to an array with a trailing comma:

Edition 5 clarifies the fact that a trailing comma at the end of an ArrayInitialiser does not add to the length of the array. This is not a semantic change from Edition 3 but some implementations may have previously misinterpreted this.

Source: http://es5.github.io/#D

[trantorLiu]

Thanks for your comments. I think I will still keep this style in my projects (front-end and back-end). Since I am using the RequireJS optimizer module which removes trailing commas, I can avoid the compatibility issues while using this syntax sugar.

[felixsanz]

@hshoff So now this changed?

[hshoff]

@felixsanz yup! we switched to Babel which removes trailing commas and we get the added benefit of cleaner diffs. https://github.com/airbnb/javascript#19.2