279 lines
10 KiB
Markdown
279 lines
10 KiB
Markdown
|
# Acorn
|
|||
|
|
|
|||
|
|
A tiny, fast JavaScript parser written in JavaScript.
|
|||
|
|
|
|||
|
|
## Community
|
|||
|
|
|
|||
|
|
Acorn is open source software released under an
|
|||
|
|
[MIT license](https://github.com/acornjs/acorn/blob/master/acorn/LICENSE).
|
|||
|
|
|
|||
|
|
You are welcome to
|
|||
|
|
[report bugs](https://github.com/acornjs/acorn/issues) or create pull
|
|||
|
|
requests on [github](https://github.com/acornjs/acorn). For questions
|
|||
|
|
and discussion, please use the
|
|||
|
|
[Tern discussion forum](https://discuss.ternjs.net).
|
|||
|
|
|
|||
|
|
## Installation
|
|||
|
|
|
|||
|
|
The easiest way to install acorn is from [`npm`](https://www.npmjs.com/):
|
|||
|
|
|
|||
|
|
```sh
|
|||
|
|
npm install acorn
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
Alternately, you can download the source and build acorn yourself:
|
|||
|
|
|
|||
|
|
```sh
|
|||
|
|
git clone https://github.com/acornjs/acorn.git
|
|||
|
|
cd acorn
|
|||
|
|
npm install
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
## Interface
|
|||
|
|
|
|||
|
|
**parse**`(input, options)` is the main interface to the library. The
|
|||
|
|
`input` parameter is a string, `options` must be an object setting
|
|||
|
|
some of the options listed below. The return value will be an abstract
|
|||
|
|
syntax tree object as specified by the [ESTree
|
|||
|
|
spec](https://github.com/estree/estree).
|
|||
|
|
|
|||
|
|
```javascript
|
|||
|
|
let acorn = require("acorn");
|
|||
|
|
console.log(acorn.parse("1 + 1", {ecmaVersion: 2020}));
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
When encountering a syntax error, the parser will raise a
|
|||
|
|
`SyntaxError` object with a meaningful message. The error object will
|
|||
|
|
have a `pos` property that indicates the string offset at which the
|
|||
|
|
error occurred, and a `loc` object that contains a `{line, column}`
|
|||
|
|
object referring to that same position.
|
|||
|
|
|
|||
|
|
Options are provided by in a second argument, which should be an
|
|||
|
|
object containing any of these fields (only `ecmaVersion` is
|
|||
|
|
required):
|
|||
|
|
|
|||
|
|
- **ecmaVersion**: Indicates the ECMAScript version to parse. Must be
|
|||
|
|
either 3, 5, 6 (or 2015), 7 (2016), 8 (2017), 9 (2018), 10 (2019),
|
|||
|
|
11 (2020), 12 (2021), 13 (2022), 14 (2023), or `"latest"` (the
|
|||
|
|
latest the library supports). This influences support for strict
|
|||
|
|
mode, the set of reserved words, and support for new syntax
|
|||
|
|
features.
|
|||
|
|
|
|||
|
|
**NOTE**: Only 'stage 4' (finalized) ECMAScript features are being
|
|||
|
|
implemented by Acorn. Other proposed new features must be
|
|||
|
|
implemented through plugins.
|
|||
|
|
|
|||
|
|
- **sourceType**: Indicate the mode the code should be parsed in. Can be
|
|||
|
|
either `"script"` or `"module"`. This influences global strict mode
|
|||
|
|
and parsing of `import` and `export` declarations.
|
|||
|
|
|
|||
|
|
**NOTE**: If set to `"module"`, then static `import` / `export` syntax
|
|||
|
|
will be valid, even if `ecmaVersion` is less than 6.
|
|||
|
|
|
|||
|
|
- **onInsertedSemicolon**: If given a callback, that callback will be
|
|||
|
|
called whenever a missing semicolon is inserted by the parser. The
|
|||
|
|
callback will be given the character offset of the point where the
|
|||
|
|
semicolon is inserted as argument, and if `locations` is on, also a
|
|||
|
|
`{line, column}` object representing this position.
|
|||
|
|
|
|||
|
|
- **onTrailingComma**: Like `onInsertedSemicolon`, but for trailing
|
|||
|
|
commas.
|
|||
|
|
|
|||
|
|
- **allowReserved**: If `false`, using a reserved word will generate
|
|||
|
|
an error. Defaults to `true` for `ecmaVersion` 3, `false` for higher
|
|||
|
|
versions. When given the value `"never"`, reserved words and
|
|||
|
|
keywords can also not be used as property names (as in Internet
|
|||
|
|
Explorer's old parser).
|
|||
|
|
|
|||
|
|
- **allowReturnOutsideFunction**: By default, a return statement at
|
|||
|
|
the top level raises an error. Set this to `true` to accept such
|
|||
|
|
code.
|
|||
|
|
|
|||
|
|
- **allowImportExportEverywhere**: By default, `import` and `export`
|
|||
|
|
declarations can only appear at a program's top level. Setting this
|
|||
|
|
option to `true` allows them anywhere where a statement is allowed,
|
|||
|
|
and also allows `import.meta` expressions to appear in scripts
|
|||
|
|
(when `sourceType` is not `"module"`).
|
|||
|
|
|
|||
|
|
- **allowAwaitOutsideFunction**: If `false`, `await` expressions can
|
|||
|
|
only appear inside `async` functions. Defaults to `true` in modules
|
|||
|
|
for `ecmaVersion` 2022 and later, `false` for lower versions.
|
|||
|
|
Setting this option to `true` allows to have top-level `await`
|
|||
|
|
expressions. They are still not allowed in non-`async` functions,
|
|||
|
|
though.
|
|||
|
|
|
|||
|
|
- **allowSuperOutsideMethod**: By default, `super` outside a method
|
|||
|
|
raises an error. Set this to `true` to accept such code.
|
|||
|
|
|
|||
|
|
- **allowHashBang**: When this is enabled, if the code starts with the
|
|||
|
|
characters `#!` (as in a shellscript), the first line will be
|
|||
|
|
treated as a comment. Defaults to true when `ecmaVersion` >= 2023.
|
|||
|
|
|
|||
|
|
- **checkPrivateFields**: By default, the parser will verify that
|
|||
|
|
private properties are only used in places where they are valid and
|
|||
|
|
have been declared. Set this to false to turn such checks off.
|
|||
|
|
|
|||
|
|
- **locations**: When `true`, each node has a `loc` object attached
|
|||
|
|
with `start` and `end` subobjects, each of which contains the
|
|||
|
|
one-based line and zero-based column numbers in `{line, column}`
|
|||
|
|
form. Default is `false`.
|
|||
|
|
|
|||
|
|
- **onToken**: If a function is passed for this option, each found
|
|||
|
|
token will be passed in same format as tokens returned from
|
|||
|
|
`tokenizer().getToken()`.
|
|||
|
|
|
|||
|
|
If array is passed, each found token is pushed to it.
|
|||
|
|
|
|||
|
|
Note that you are not allowed to call the parser from the
|
|||
|
|
callback—that will corrupt its internal state.
|
|||
|
|
|
|||
|
|
- **onComment**: If a function is passed for this option, whenever a
|
|||
|
|
comment is encountered the function will be called with the
|
|||
|
|
following parameters:
|
|||
|
|
|
|||
|
|
- `block`: `true` if the comment is a block comment, false if it
|
|||
|
|
is a line comment.
|
|||
|
|
- `text`: The content of the comment.
|
|||
|
|
- `start`: Character offset of the start of the comment.
|
|||
|
|
- `end`: Character offset of the end of the comment.
|
|||
|
|
|
|||
|
|
When the `locations` options is on, the `{line, column}` locations
|
|||
|
|
of the comment’s start and end are passed as two additional
|
|||
|
|
parameters.
|
|||
|
|
|
|||
|
|
If array is passed for this option, each found comment is pushed
|
|||
|
|
to it as object in Esprima format:
|
|||
|
|
|
|||
|
|
```javascript
|
|||
|
|
{
|
|||
|
|
"type": "Line" | "Block",
|
|||
|
|
"value": "comment text",
|
|||
|
|
"start": Number,
|
|||
|
|
"end": Number,
|
|||
|
|
// If `locations` option is on:
|
|||
|
|
"loc": {
|
|||
|
|
"start": {line: Number, column: Number}
|
|||
|
|
"end": {line: Number, column: Number}
|
|||
|
|
},
|
|||
|
|
// If `ranges` option is on:
|
|||
|
|
"range": [Number, Number]
|
|||
|
|
}
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
Note that you are not allowed to call the parser from the
|
|||
|
|
callback—that will corrupt its internal state.
|
|||
|
|
|
|||
|
|
- **ranges**: Nodes have their start and end characters offsets
|
|||
|
|
recorded in `start` and `end` properties (directly on the node,
|
|||
|
|
rather than the `loc` object, which holds line/column data. To also
|
|||
|
|
add a
|
|||
|
|
[semi-standardized](https://bugzilla.mozilla.org/show_bug.cgi?id=745678)
|
|||
|
|
`range` property holding a `[start, end]` array with the same
|
|||
|
|
numbers, set the `ranges` option to `true`.
|
|||
|
|
|
|||
|
|
- **program**: It is possible to parse multiple files into a single
|
|||
|
|
AST by passing the tree produced by parsing the first file as the
|
|||
|
|
`program` option in subsequent parses. This will add the toplevel
|
|||
|
|
forms of the parsed file to the "Program" (top) node of an existing
|
|||
|
|
parse tree.
|
|||
|
|
|
|||
|
|
- **sourceFile**: When the `locations` option is `true`, you can pass
|
|||
|
|
this option to add a `source` attribute in every node’s `loc`
|
|||
|
|
object. Note that the contents of this option are not examined or
|
|||
|
|
processed in any way; you are free to use whatever format you
|
|||
|
|
choose.
|
|||
|
|
|
|||
|
|
- **directSourceFile**: Like `sourceFile`, but a `sourceFile` property
|
|||
|
|
will be added (regardless of the `location` option) directly to the
|
|||
|
|
nodes, rather than the `loc` object.
|
|||
|
|
|
|||
|
|
- **preserveParens**: If this option is `true`, parenthesized expressions
|
|||
|
|
are represented by (non-standard) `ParenthesizedExpression` nodes
|
|||
|
|
that have a single `expression` property containing the expression
|
|||
|
|
inside parentheses.
|
|||
|
|
|
|||
|
|
**parseExpressionAt**`(input, offset, options)` will parse a single
|
|||
|
|
expression in a string, and return its AST. It will not complain if
|
|||
|
|
there is more of the string left after the expression.
|
|||
|
|
|
|||
|
|
**tokenizer**`(input, options)` returns an object with a `getToken`
|
|||
|
|
method that can be called repeatedly to get the next token, a `{start,
|
|||
|
|
end, type, value}` object (with added `loc` property when the
|
|||
|
|
`locations` option is enabled and `range` property when the `ranges`
|
|||
|
|
option is enabled). When the token's type is `tokTypes.eof`, you
|
|||
|
|
should stop calling the method, since it will keep returning that same
|
|||
|
|
token forever.
|
|||
|
|
|
|||
|
|
In ES6 environment, returned result can be used as any other
|
|||
|
|
protocol-compliant iterable:
|
|||
|
|
|
|||
|
|
```javascript
|
|||
|
|
for (let token of acorn.tokenizer(str)) {
|
|||
|
|
// iterate over the tokens
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
// transform code to array of tokens:
|
|||
|
|
var tokens = [...acorn.tokenizer(str)];
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
**tokTypes** holds an object mapping names to the token type objects
|
|||
|
|
that end up in the `type` properties of tokens.
|
|||
|
|
|
|||
|
|
**getLineInfo**`(input, offset)` can be used to get a `{line,
|
|||
|
|
column}` object for a given program string and offset.
|
|||
|
|
|
|||
|
|
### The `Parser` class
|
|||
|
|
|
|||
|
|
Instances of the **`Parser`** class contain all the state and logic
|
|||
|
|
that drives a parse. It has static methods `parse`,
|
|||
|
|
`parseExpressionAt`, and `tokenizer` that match the top-level
|
|||
|
|
functions by the same name.
|
|||
|
|
|
|||
|
|
When extending the parser with plugins, you need to call these methods
|
|||
|
|
on the extended version of the class. To extend a parser with plugins,
|
|||
|
|
you can use its static `extend` method.
|
|||
|
|
|
|||
|
|
```javascript
|
|||
|
|
var acorn = require("acorn");
|
|||
|
|
var jsx = require("acorn-jsx");
|
|||
|
|
var JSXParser = acorn.Parser.extend(jsx());
|
|||
|
|
JSXParser.parse("foo(<bar/>)", {ecmaVersion: 2020});
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
The `extend` method takes any number of plugin values, and returns a
|
|||
|
|
new `Parser` class that includes the extra parser logic provided by
|
|||
|
|
the plugins.
|
|||
|
|
|
|||
|
|
## Command line interface
|
|||
|
|
|
|||
|
|
The `bin/acorn` utility can be used to parse a file from the command
|
|||
|
|
line. It accepts as arguments its input file and the following
|
|||
|
|
options:
|
|||
|
|
|
|||
|
|
- `--ecma3|--ecma5|--ecma6|--ecma7|--ecma8|--ecma9|--ecma10`: Sets the ECMAScript version
|
|||
|
|
to parse. Default is version 9.
|
|||
|
|
|
|||
|
|
- `--module`: Sets the parsing mode to `"module"`. Is set to `"script"` otherwise.
|
|||
|
|
|
|||
|
|
- `--locations`: Attaches a "loc" object to each node with "start" and
|
|||
|
|
"end" subobjects, each of which contains the one-based line and
|
|||
|
|
zero-based column numbers in `{line, column}` form.
|
|||
|
|
|
|||
|
|
- `--allow-hash-bang`: If the code starts with the characters #! (as
|
|||
|
|
in a shellscript), the first line will be treated as a comment.
|
|||
|
|
|
|||
|
|
- `--allow-await-outside-function`: Allows top-level `await` expressions.
|
|||
|
|
See the `allowAwaitOutsideFunction` option for more information.
|
|||
|
|
|
|||
|
|
- `--compact`: No whitespace is used in the AST output.
|
|||
|
|
|
|||
|
|
- `--silent`: Do not output the AST, just return the exit status.
|
|||
|
|
|
|||
|
|
- `--help`: Print the usage information and quit.
|
|||
|
|
|
|||
|
|
The utility spits out the syntax tree as JSON data.
|
|||
|
|
|
|||
|
|
## Existing plugins
|
|||
|
|
|
|||
|
|
- [`acorn-jsx`](https://github.com/RReverser/acorn-jsx): Parse [Facebook JSX syntax extensions](https://github.com/facebook/jsx)
|