Proposal: Require trailing commas for multiline objects

[robertrossmann]

I propose that we start requiring trailing commas for multiline objects. Currently trailing commas are optional. Single-line object literals will not be affected by this change.

This rule can be auto-fixed by ESLint, therefore no manual changes are required in your code.

Current

const obj = {
  first: 1,
  second: 2  // Here, the comma is optional
}

New

const obj = {
  first: 1,
  second: 2,  // Here, the comma is required
}

Why?

• Every time you want to add a new property to an object, you have to remember to put the trailing comma to the preceding property, otherwise you get a syntax error. Enforcing the comma to already be there, you mitigate this completely.
• git diffs will look more clean, because you now do not have to edit an unrelated line to introduce your changes.
• It is easier to sort the object's properties with just F5 or similar editor tool

Please vote 👍 or 👎 via reaction or leave a comment if you have questions or suggestions. Thanks!

[Milan4e]

Counter proposal:

const obj = {
  first: 1
  ,second: 2
  ,third: 3
  ,forth: 4
}

P.S I am serious

[jzavisek]

I think this will not help with lines sorting :(

[robertrossmann]

@Milan4e I actually wrote code like that some time ago! I personally liked that style, but the problem was with tooling - some tools (ie. docblock parsers) do not cope well with the comma being at the next line. Example:

const obj = {
  /**
   * Document for first
   * @type    {String}
   */
  first: 'test'
  /**
   * A trailing docblock for first!
   * @type    {String}
   */
, second: 'test again'
}

[robertrossmann]

Next major version (6.0) of js-coding-standards will require trailing commas for multiline object/array expressions.

Please note that this rule can be autofixed by ESLint itself - updating your codebase should therefore be as trivial as running node_modules/.bin/eslint --fix . from your project's directory.

Thank you all for your feedback!