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docs: add attachComment #2555

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Aug 4, 2021
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docs: add attachComment #2555

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docs: add attachComment
JLHwung Jul 14, 2021
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JLHwung Jul 14, 2021
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4 changes: 4 additions & 0 deletions docs/parser.md
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Expand Up @@ -33,6 +33,7 @@ mind. When in doubt, use `.parse()`.
<summary>History</summary>
| Version | Changes |
| --- | --- |
| `v7.15.0` | Added `attachComment` |
| `v7.7.0` | Added `errorRecovery` |
| `v7.5.0` | Added `allowUndeclaredExports` |
| `v7.2.0` | Added `createParenthesizedExpressions` |
Expand Down Expand Up @@ -64,6 +65,8 @@ mind. When in doubt, use `.parse()`.
to set this option to `true` to prevent the parser from prematurely
complaining about undeclared exports that will be added later.

- **attachComment**: By default, Babel attaches comments to adjacent AST nodes. When this option is set to `false`, comments are not attached. It can provide up to 30% performance improvement when the input code has _many_ comments. `@babel/eslint-parser` will set it for you. It is not recommended to use `attachComment: false` with Babel transform, as doing so removes all the comments in output code, and renders annotations such as `/* istanbul ignore next */` nonfunctional.

- **createParenthesizedExpressions**: By default, the parser sets `extra.parenthesized` on the expression nodes. When this option is set to `true`, `ParenthesizedExpression` AST nodes are created instead.

- **errorRecovery**: By default, Babel always throws an error when it finds some invalid
Expand Down Expand Up @@ -278,6 +281,7 @@ You should enable these features only if you are using an older version.
See [Ergonomics of `#{}`/`#[]`](https://github.com/tc39/proposal-record-tuple/issues/10) for more information.

- `flow`:

- `all` (`boolean`, default: `false`)
Some code has different meaning in Flow and in vanilla JavaScript. For example, `foo<T>(x)` is parsed as a call expression with a type argument in Flow, but as a comparison (`foo < T > x`) accordingly to the ECMAScript specification. By default, `babel-parser` parses those ambiguous constructs as Flow types only if the file starts with a `// @flow` pragma.
Set this option to `true` to always parse files as if `// @flow` was specified.
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