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prettier-plugin-insert-comma

A Prettier plugin that automatically inserts missing commas in multi-line object properties before formatting.

Prettier cannot format code with syntax errors like missing commas in objects. This plugin runs as a preprocessor to insert commas between properties, allowing Prettier to format your code successfully.

The plugin first checks the original source with Prettier's language parser. If the parser reports a missing comma, it inserts a separator and checks again. This preserves literal contents, including regular expressions, JSX text, and nested template strings. Comments, shorthand properties, methods, numeric and Unicode keys are supported. Trailing commas are left to Prettier's settings.

Recovery requires another parse for each missing comma and is limited to 100 insertions per file. If recovery fails or reaches that limit without producing valid syntax, the original source is passed back to Prettier for its normal error reporting. Other syntax errors are not repaired.

Requirements

• Prettier 3.7.0 or higher

Example

Before — Prettier would throw a parse error:

const config = {
  host: 'localhost'
  port: 3000
  options: {
    debug: true
    verbose: false
  }
}

After — commas are inserted, Prettier formats normally:

const config = {
  host: 'localhost',
  port: 3000,
  options: {
    debug: true,
    verbose: false,
  },
};

Installation

Install prettier-plugin-insert-comma as a dev dependency:

npm install -D prettier prettier-plugin-insert-comma

Then add the plugin to your Prettier configuration:

// .prettierrc
{
  "plugins": ["prettier-plugin-insert-comma"],
}

For JSON files, you need to specify the parser explicitly with overrides:

{
  "plugins": ["prettier-plugin-insert-comma"],
  "overrides": [
    {
      "files": ["*.json"],
      "options": {
        "parser": "json",
        "quoteProps": "preserve",
        "singleQuote": false,
        "trailingComma": "none"
      }
    }
  ]
}

Supported Languages

Language
TypeScript, TSX
JavaScript, JSX
JSON