Allow non-identifiers to be used for JSXFragmentFactory

Search Terms

JSX factory expression identifier string JSXFragmentFactory

Related Issues

https://github.com/Microsoft/TypeScript/issues/20469
https://github.com/microsoft/TypeScript/pull/38720

Suggestion

Allow non-identifiers to be used as the JSXFragmentFactory. Currently, attempting to use a non-identifier like the empty string results in the following error:

  tsconfig.json(9,27): error TS18035: Invalid value for 'jsxFragmentFactory'. '''' is not a valid identifier or qualified-name.

My config:

{
  "include": ["src", "types"],
  "compilerOptions": {
    "module": "esnext",
    "target": "esnext",
    "moduleResolution": "node",
    "jsx": "preserve",
    "jsxFactory": "createElement",
    "jsxFragmentFactory": "''",
    "lib": ["esnext", "dom"],
    "baseUrl": "./",
    /* paths - If you configure Snowpack import aliases, add them here. */
    "paths": {},
    /* noEmit - Snowpack builds (emits) files, not tsc. */
    "noEmit": true,
    /* Additional Options */
    "strict": true,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true,
    "resolveJsonModule": true,
    "allowSyntheticDefaultImports": true,
    "importsNotUsedAsValues": "error"
  }
}

Use Cases

My JSX framework defines the Fragment tag as the empty string. Babel’s JSX support allows non-identifiers to be used as the JSXFragmentFactory so I wonder why we can’t do the same in TypeScript.

Using an identifier is a little more awkward.

Examples

With the jsxFactory set to createElement and the jsxFragmentFactory set to the empty string, emitted code might look like the following.

createElement(
  "",
  null,
  createElement("div", null),
  createElement("div", null),
);

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

Start by reviewing the jsxFragmentFactory compiler option validation and the related issue and pull request linked in the report. Done means non-identifier values such as the empty string are accepted and JSX fragments emit using the configured factory without the current invalid-identifier error.