Git: The Trailing Comma Journey

Comma

Comma U+002C in programming language, usually used to separating each item of a list or a hash. The common usage in programming language is to place comma in between item on a list. e.g:

fruits = ['apple', 'banana', 'mango']

In Ruby, Python, and JavaScript the syntax above is valid. But for list with item that has a long name. Locating a specific item will be tedious. Another way to format it is by separating each item into separate line.

fruits = [
  'apple',
  'banana',
  'mango'
]

With this format, secifying an item is easy, especially if the item is sorted. The downside of this format is if we want to add new item, we requires edit 2 lines, the first 1 is adding comma at the end of the last item (‘Manggo’). Then adding a new item itself in new line.

New Item of an Array and Git

For Git, the new Item will add unnecessary changes in the last item of the list. The solution of this is to adding a trailing comma to the last item of the list.

fruits = [
  'apple',
  'banana',
  'mango',
]

Enforce Trailing Comma

We can enforce this style using a linter, on eslint you can specify comma-dangle config:

{
    "rules": {
      "comma-dangle": ["error", {
        "arrays": "always-multiline",
        "objects": "always-multiline",
      }]
    }
}

This will raises error if there is a multiline array or hash that doesn’t have a trailing comma.

Coala Pull Request with this issue