tsconfig.json actually supports trailing commas

[DecimalTurn]

The draft spec was recently edited to include reasons why trailing commas should not be supported. A major reason that was mentioned multiple times in issues/discussion in the VS Code repo is that tsconfig.json doesn't support trailing commas.

However, this last statement is incorrect. tsconfig.json files do support trailing commas according to the schema on schemastore.

Note

Because VS Code automatically uses the tsconfig schema for tsconfig.json file, it won't show a warning for tsconfig.json files with trailing commas.

{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "$comment": "Note that this schema uses 'null' in various places. The value of 'null' is UNDOCUMENTED (https://github.com/microsoft/TypeScript/pull/18058)",
  "allowTrailingCommas": true,
  "allOf": [
	...

Hence, considering the following... :

• The official Typescript tsconfig parser supports it (source).
• 2 out of the 3 most popular npm packages used to parse tsconfig files support it:
  • 🟢 https://www.npmjs.com/package/get-tsconfig ✅
  • 🔵 https://www.npmjs.com/package/tsconfck ✅
  • 🟠 https://www.npmjs.com/package/tsconfig ❌ (unmaintained)

... we should should consider removing the mention that tsconfig.json doesn't support trailing commas.

[ell1e]

I still think that JSONC doesn't make much sense without trailing commas by default, given the VS Code UI accepts them and even seems to encourage them for the VS Code config.

However, the official node-jsonc-parser still defaults to disabling them and there's no maintainer response so far. So I guess it's still up in the air, if that's what we want to depend on.

[DecimalTurn]

Considering that .eslintrc.json is now depreciated , I'm not aware of any important actively supported JSONC configuration file that doesn't support trailing commas. This makes me think that the position on trailing commas in this spec needs to change, but I haven't settled on the exact wording yet.

[silverwind]

Most if not all JSONC parsers support trailing commas by default. The spec needs to change imho.

• tsconfig always supported it (to my knowledge)
• vscode always supported it
• sublime text always supported it
• devcontainers configs support it

I noticed this is that I recently configures this linter which currently does not enable trailing commas by default.

[DecimalTurn]

Most if not all JSONC parsers support trailing commas by default.

@silverwind How do you measure that? Did you count the number of parsers that support trailing commas (TC) by default out of all the parsers out there? Because the main parser jsonc-parser doesn't support them by default.

https://github.com/microsoft/node-jsonc-parser/blob/05d66ec1d36df933406c99fd698a79db91a2d804/src/impl/parser.ts#L22-L26

namespace ParseOptionsConfigs {
	export const DEFAULT = {
		allowTrailingComma: false
	};
}

---

tsconfig always supported it (to my knowledge)

It seems like Typescript introduced TC support accidently in v2.5 (2017). Looking at the original PR, you can even see a comment from a now deleted user saying that they should return an error for trailing commas:

Those comments were supposed to be followed-up in this issue, but they were never addressed properly.

Also note that there is no mention of trailing commas in the announcement of TypeScript 2.5: What's new in TypeScript 2.5

---

vscode always supported it

I'm pretty sure we can find and old version of VS Code that doesn't support TC, but we can agree that it's been a while.

---

sublime text always supported it

Among all the claims in your comment, I'm mostly interested in this one. Do you have more details about how Sublime supports trailing commas? I couldn't find any official documentation.

---

devcontainers configs support it

The official schema says otherwise. It contains:

"allowTrailingCommas": false,

[fictiontoreality]

It is a shame a broadly used serialization standard is defined by quirks of IDEs and JavaScript. It should be the other way around. The only value I can see for the standard is encouraging the standards you want to see, rather than reiterating the lack of standards that exist.

[ell1e]

I somewhat agree with @fictiontoreality as you can see here. (Sorry if this remark is superfluous and was obvious.)