fix: jsx is undefined by default, not preserve or react (#1102)

* fix: `jsx` is undefined by default, not preserve or react

- one gets an error when using JSX without configuring `jsx`:
  `error TS17004: Cannot use JSX unless the '--jsx' flag is provided.`

- TSConfig Reference said default was `react`, which is inaccurate
- Compiler Options said default was `preserve`, which is also inaccurate

- Add a `undefined` as the default in TSConfig Reference, same as
  allowUnrechableCode
- Remove the default in Compiler Options, same as all the other options
  without defaults

----
History:

Reference:
- `preserve` was written as the default in eae5cc3#diff-444415c73770eafd0f9db7d708d74131R5
- But then was written as `react` in the body in eae5cc3#diff-444415c73770eafd0f9db7d708d74131R5
- It was then switched to `react` in 450ae96#diff-a912c6af3a16bf4288093c1264955bc6R120
- And then removed in 76b7d43#diff-a912c6af3a16bf4288093c1264955bc6L120

Compiler Options:
- `preserve` was written as the default in 66f17ad#diff-bfc78b96c15b0ee906c1ab6176546dceR41

* Update Compiler Options.md

* Update Compiler Options.md

Co-authored-by: Orta Therox <ortam@microsoft.com>
Co-authored-by: Orta Therox <git@orta.io>

Author: 3 people

packages/documentation/copy/en/project-config/Compiler Options.md

@@ -65,7 +65,7 @@ Option                                         | Type      | Default
 `--inlineSources`                              | `boolean` | `false`                        | Emit the source alongside the sourcemaps within a single file; requires `--inlineSourceMap` or `--sourceMap` to be set.
 `--init`                                       |           |                                | Initializes a TypeScript project and creates a `tsconfig.json` file.
 `--isolatedModules`                            | `boolean` | `false`                        | Perform additional checks to ensure that separate compilation (such as with [`transpileModule`](https://github.com/Microsoft/TypeScript/wiki/Using-the-Compiler-API#a-simple-transform-function) or [@babel/plugin-transform-typescript](https://babeljs.io/docs/en/babel-plugin-transform-typescript)) would be safe.
-`--jsx`                                        | `string`  | `"preserve"`                   | Support JSX in `.tsx` files: `"react"`, `"preserve"`, `"react-native"`. See [JSX](/docs/handbook/jsx.html).
+`--jsx`                                        | `string`  |                                | Support JSX in `.tsx` files: `"react"`, `"preserve"`, `"react-native"`. See [JSX](/docs/handbook/jsx.html).
 `--jsxFactory`                                 | `string`  | `"React.createElement"`        | Specify the JSX factory function to use when targeting react JSX emit, e.g. `React.createElement` or `h`.
 `--jsxFragmentFactory`                         | `string`  | `"React.Fragment"`             | Specify the JSX fragment factory function to use when targeting react JSX emit, e.g. `Fragment`.
 `--keyofStringsOnly`                           | `boolean` | `false`                        | Resolve `keyof` to string valued property names only (no numbers or symbols).

packages/tsconfig-reference/scripts/tsconfigRules.ts

@@ -135,6 +135,7 @@ export const defaultsForOptions = {
   inlineSourceMap: "false",
   inlineSources: "false",
   isolatedModules: "false",
+  jsx: "undefined",
   jsxFactory: "`React.createElement`",
   keyofStringsOnly: "false",
   listEmittedFiles: "false",
@@ -186,7 +187,7 @@ export const defaultsForOptions = {
 };
 
 export const allowedValues = {
-  jsx: ["`react` (default)", "`react-native`", "`preserve`"],
+  jsx: ["`react`", "`react-native`", "`preserve`"],
   jsxFactory: ["Any identifier or dotted identifier"],
   lib: ["See main content"],
   target: [