astx

Super powerful structural search and replace for JavaScript and TypeScript to automate your refactoring

Introduction

Simple refactors can be tedious and repetitive. For example say you want to make the following change across a codebase:

// before:
rmdir('old/stuff')
rmdir('new/stuff', true)

// after:
rmdir('old/stuff')
rmdir('new/stuff', { force: true })

Changing a bunch of calls to rmdir by hand would suck. You could try using regex replace, but it's fiddly and wouldn't tolerate whitespace and linebreaks well unless you work really hard at the regex. You could even use jscodeshift, but it takes too long for simple cases like this, and starts to feel harder than necessary...

Now there's a better option...you can refactor with confidence using astx!

astx \
  --find    'rmdir($path, $force)' \
  --replace 'rmdir($path, { force: $force })'

This is a basic example of astx patterns, which are just JS or TS code that can contain placeholders and other special matching constructs; astx looks for code matching the pattern, accepting any expression in place of $path and $force. Then astx replaces each match with the replace pattern, substituting the expressions it captured for $path ('new/stuff') and $force (true).

But this is just the beginning; astx patterns can be much more complex and powerful than this, and for really advanced use cases it has an intuitive API you can use:

for (const match of astx.find`rmdir($path, $force)`) {
  const { $path, $force } = match
  // do stuff with $path.node, $path.code, etc...
}

Usage examples

Fixing eslint errors

Got a lot of Do not access Object.prototype method 'hasOwnProperty' from target object errors?

// astx.js
exports.find = `$a.hasOwnProperty($b)`
exports.replace = `Object.hasOwn($a, $b)`

Restructure array concatenation

Recently for work I wanted to make this change:

// before
const pkg = OrgPackage({
  subPackage: [
    'services',
    async ? 'async' : 'blocking',
    ...namespace,
    Names.ServiceType({ resource, async }),
  ],
})

// after
const pkg = [
  ...OrgPackage(),
  'services',
  async ? 'async' : 'blocking',
  ...namespace,
  Names.ServiceType({ resource, async }),
]

This is simple to do with list matching:

// astx.js
exports.find = `OrgPackage({subPackage: [$$p]})`
exports.replace = `[...OrgPackage(), $$p]`

Convert require statements to imports

// astx.js
exports.find = `const $id = require('$source')`
exports.replace = `import $id from '$source'`

Combine unnecessary nested if statements

// astx.js
export const find = `if ($a) { if ($b) $body }`
export const replace = `if ($a && $b) $body`

Make code DRY

In jscodeshift-add-imports I had a bunch of test cases following this pattern:

it(`leaves existing default imports untouched`, function () {
  const code = `import Baz from 'baz'`
  const root = j(code)
  const result = addImports(root, statement`import Foo from 'baz'`)
  expect(result).to.deep.equal({ Foo: 'Baz' })
  expect(root.toSource()).to.equal(code)
})

I wanted to make them more DRY, like this:

it(`leaves existing default imports untouched`, function () {
  testCase({
    code: `import Baz from 'baz'`,
    add: `import Foo from 'baz'`,
    expectedCode: `import Baz from 'baz'`,
    expectedReturn: { Foo: 'Baz' },
  })
})

Here was a transform for the above. (Of course, I had to run a few variations of this for cases where the expected code was different, etc.)

exports.find = `
const code = $code
const root = j(code)
const result = addImports(root, statement\`$add\`)
expect(result).to.deep.equal($expectedReturn)
expect(root.toSource()).to.equal(code)
`

exports.replace = `
testCase({
  code: $code,
  add: \`$add\`,
  expectedCode: $code,
  expectedReturn: $expectedReturn,
})
`

Roadmap

I just finally got version 2 released as of December 2022 after tons of hard work 🎉 Right now I'm working on the VSCode Extension. After that I want to make a documentation website that better illustrates how to use astx.

VSCode Extension

The VSCode Extension is currently in beta, but try it out!

Prior art and philosophy

While I was thinking about making this I discovered grasp, a similar tool that inspired the $ capture syntax. There are several reasons I decided to make astx anyway:

Grasp uses the Acorn parser, which doesn't support TypeScript or Flow code AFAIK
Hasn't been updated in 4 years
Grasp's replace pattern syntax is clunkier, doesn't match the find pattern syntax: grasp -e 'setValue($k, $v, true)' -R 'setValueSilently({{k}}, {{v}})' file.js
It has its own DSL (SQuery) that's pretty limited and has a slight learning curve
I wanted a jscodeshift-like API I could use in JS for advanced use cases that are probably awkward/impossible in Grasp

So the philosophy of astx is:

Provide a simple find and replace pattern syntax that's ideal for simple cases and has minimum learning curve
Use the same search and replace pattern syntax in the javascript API for anything more complex, so that you have unlimited flexibility

Paste your code into AST Explorer if you need to learn about the structure of the AST.

Pattern Language

Astx find patterns are just JavaScript or TypeScript code that may contain placeholder wildcards or other special constructs like $Or(A, B). Generally speaking, parts of the pattern that aren't wildcards or special constructs have to match exactly.

For example, the find pattern foo($a) matches any call to the function foo with a single argument. The argument can anything and is captured as $a.

Replace patterns are almost identical to find patterns, except that placeholders get replaced with whatever was captured into the placeholder name by the find pattern, and special find constructs like $Or(A, B) have no special meaning in replace patterns. (In the future, there may be special replace constructs that perform some kind of transformation on captured nodes.)

For example, the find pattern foo($a) matches foo(1 + 2), then the replace pattern foo({ value: $a }) will generate the code foo({ value: 1 + 2 }).

Placeholders

Generally speaking, an identifier starting with $ is a placeholder that functions like a wildcard. There are three types of placeholders:

$<name> matches any single node ("node placeholder")
$$<name> matches a contiguous list of nodes ("array placeholder")
$$$<name>: matches all other siblings ("rest placeholder")

The <name> (if given) must start with a letter or number; otherwise the identifier will not be treated as a placeholder.

Rest placeholders ($$$) may not be sibilings of ordered list placeholders ($$).

Unless a placeholder is anonymous, it will "capture" the matched node(s), meaning you can use the same placeholder in the replacement pattern to interpolate the matched node(s) into the generated replacement. In the Node API you can also access the captured AST paths/nodes via the placeholder name.

Node Placeholders (`$<name>`)

These placeholders match a single node. For example, the pattern [$a, $b] matches an array expression with two elements, and those elements are captured as $a and $b.

Array Placeholders (`$$<name>`)

These placeholders match a contiguous list of nodes. For example, the pattern [1, $$a, 2, $$b] matches an array expression with 1 as the first element, and 2 as a succeeding element. Any elements between 1 and the first 2 is captured as $$a, and elements after the first 2 are captured as $$b.

Rest Placeholders (`$$$<name>`)

These placeholders match the rest of the siblings that weren't matched by something else. For example, the pattern [1, $$$a, 2] matches an array expression that has elements 1 and 2 at any index. Any other elements (including additional occurrences of 1 and 2) are captured as $$$a.

Anonymous Placeholders

You can use a placeholder without a name to match node(s) without capturing them. $ will match any single node, $$ will match a contiguous list of nodes, and $$$ will match all other siblings.

Backreferences

If you use the same capture placeholder more than once, subsequent positions will have to match what was captured for the first occurrence of the placeholder.

For example, the pattern foo($a, $a, $b, $b) will match only foo(1, 1, {foo: 1}, {foo: 1}) in the following:

foo(1, 1, { foo: 1 }, { foo: 1 }) // match
foo(1, 2, { foo: 1 }, { foo: 1 }) // no match
foo(1, 1, { foo: 1 }, { bar: 1 }) // no match

Note: array capture placeholders ($$a) and rest capture placeholders ($$$a) don't currently support backreferencing.

Object Matching

An ObjectExpression (aka object literal) pattern will match any ObjectExpression in your code with the same properties in any order. It will not match if there are missing or additional properties. For example, { foo: 1, bar: $bar } will match { foo: 1, bar: 2 } or { bar: 'hello', foo: 1 } but not { foo: 1 } or { foo: 1, bar: 2, baz: 3 }.

You can match additional properties by using ...$$captureName, for example { foo: 1, ...$$rest } will match { foo: 1 }, { foo: 1, bar: 2 }, { foo: 1, bar: 2, ...props } etc. The additional properties will be captured in match.arrayCaptures/match.arrayPathCaptures, and can be spread in replacement expressions. For example, astx.find`{ foo: 1, ...$$rest }`.replace`{ bar: 1, ...$$rest }` will transform { foo: 1, qux: {}, ...props } into { bar: 1, qux: {}, ...props }.

A spread property that isn't of the form /^\$\$[a-z0-9]+$/i is not a capture placeholder, for example { ...foo } will only match { ...foo } and { ...$_$foo } will only match { ...$$foo } (leading $_ is an escape for $).

There is currently no way to match properties in a specific order, but it could be added in the future.

List Matching

In many cases where there is a list of nodes in the AST you can match multiple elements with a placeholder starting with $$. For example, [$$before, 3, $$after] will match any array expression containing an element 3; elements before the first 3 will be captured in $$before and elements after the first 3 will be captured in $$after.

This works even with block statements. For example, function foo() { $$before; throw new Error('test'); $$after; } will match function foo() that contains a throw new Error('test'), and the statements before and after that throw statement will get captured in $$before and $$after, respectively.

Ordered and unordered List Matching

In some cases list matching will be ordered by default, and in some cases it will be unordered. For example, ObjectExpression property matches are unordered by default, as shown in the table below. Using a $$ placeholder or the special $Ordered placeholder will force ordered matching. Using a $$$ placeholder or the special $Unordered placeholder will force unordered matching.

If you use a placeholder starting with $$$, it's treated as a "rest" capture, and all other elements of the match expression will be matched out of order. For example, import {a, b, $$$rest} from 'foo' would match import {c, b, d, e, a} from 'foo', putting specifiers c, d, and e, into the $$$rest placeholder.

Rest placeholders ($$$) may not be sibilings of ordered list placeholders ($$).

Support Table

Some items marked TODO probably actually work, but are untested.

Type	Supports list matching?	Unordered by default?	Notes
`ArrayExpression.elements`	✅
`ArrayPattern.elements`	✅
`BlockStatement.body`	✅
`CallExpression.arguments`	✅
`Class(Declaration/Expression).implements`	✅	✅
`ClassBody.body`	✅	✅
`ComprehensionExpression.blocks`	TODO
`DeclareClass.body`	TODO	✅
`DeclareClass.implements`	TODO	✅
`DeclareExportDeclaration.specifiers`	TODO	✅
`DeclareInterface.body`	TODO
`DeclareInterface.extends`	TODO
`DoExpression.body`	TODO
`ExportNamedDeclaration.specifiers`	✅	✅
`Function.decorators`	TODO
`Function.params`	✅
`FunctionTypeAnnotation/TSFunctionType.params`	✅
`GeneratorExpression.blocks`	TODO
`ImportDeclaration.specifiers`	✅	✅
`(TS)InterfaceDeclaration.body`	TODO	✅
`(TS)InterfaceDeclaration.extends`	TODO	✅
`IntersectionTypeAnnotation/TSIntersectionType.types`	✅	✅
`JSX(Element/Fragment).children`	✅
`JSX(Opening)Element.attributes`	✅	✅
`MethodDefinition.decorators`	TODO
`NewExpression.arguments`	✅
`ObjectExpression.properties`	✅	✅
`ObjectPattern.decorators`	TODO
`ObjectPattern.properties`	✅	✅
`(ObjectTypeAnnotation/TSTypeLiteral).properties`	✅	✅	Use $a: $ to match one property, `$$a: $` or `$$$a: $` to match multiple
`Program.body`	✅
`Property.decorators`	TODO
`SequenceExpression`	✅
`SwitchCase.consequent`	✅
`SwitchStatement.cases`	TODO
`TemplateLiteral.quasis/expressions`	❓ not sure if I can come up with a syntax
`TryStatement.guardedHandlers`	TODO
`TryStatement.handlers`	TODO
`TSFunctionType.parameters`	✅
`TSCallSignatureDeclaration.parameters`	TODO
`TSConstructorType.parameters`	TODO
`TSConstructSignatureDeclaration.parameters`	TODO
`TSDeclareFunction.params`	TODO
`TSDeclareMethod.params`	TODO
`EnumDeclaration.body/TSEnumDeclaration.members`	TODO	✅
`TSIndexSignature.parameters`	TODO
`TSMethodSignature.parameters`	TODO
`TSModuleBlock.body`	TODO
`TSTypeLiteral.members`	✅	✅
`TupleTypeAnnotation/TSTupleType.types`	✅
`(TS)TypeParameterDeclaration.params`	✅
`(TS)TypeParameterInstantiation.params`	✅
`UnionTypeAnnotation/TSUnionType.types`	✅	✅
`VariableDeclaration.declarations`	✅
`WithStatement.body`	❌ who uses with statements...

String Matching

A string that's just a placeholder like '$foo' will match any string and capture its contents into match.stringCaptures.$foo. The same escaping rules apply as for identifiers. This also works for template literals like `$foo` and tagged template literals like doSomething`$foo`.

This can be helpful for working with import statements. For example, see Converting require statements to imports.

Extracting nodes

An empty comment (/**/) in a pattern will "extract" a node for matching. For example the pattern const x = { /**/ $key: $value } will just match ObjectProperty nodes against $key: $value.

The parser wouldn't be able to parse $key: $value by itself or know that you mean an ObjectProperty, as opposed to something different like the x: number in const x: number = 1, so using /**/ enables you to work around this. You can use this to match any node type that isn't a valid expression or statement by itself. For example type T = /**/ Array<number> would match Array<number> type annotations.

/**/ also works in replacement patterns.

Special Constructs

`$Maybe(pattern)`

Matches either the given expression or no node in its place. For example let $a = $Maybe(2) will match let foo = 2 and let foo (with no initializer), but not let foo = 3.

`$Or(...)`

Matches nodes that match at least one of the given patterns. For example $Or(foo($$args), {a: $value}) will match calls to foo and object literals with only an a property.

`$And(...)`

Matches nodes that match all of the given patterns. This is mostly useful for narrowing down the types of nodes that can be captured into a given placeholder. For example, let $a = $And($init, $a + $b) will match let declarations where the initializer matches $a + $b, and capture the initializer as $init.

`$Maybe<pattern>`

Matches either the given type annotation or no node in its place. For example let $a: $Maybe<number> will match let foo: number and let foo (with no type annotation), but not let foo: string``let foo: string.

`$Or<...>`

Matches nodes that match at least one of the given type annotations. For example let $x: $Or<number[], string[]> will match let declarations of type number[] or string[].

`$And<...>`

Matches nodes that match all of the given type annotations. This is mostly useful for narrowing down the types of nodes that can be captured into a given placeholder. For example, let $a: $And<$type, $elem[]> will match let declarations where the type annotation matches $elem[], and capture the type annotation as $type.

`$Ordered`

Forces the pattern to match sibling nodes in the same order.

`$Unordered`

Forces the pattern to match sibling nodes in any order.

API

interface NodePath

import { NodePath } from 'astx'

This is the same NodePath interface as ast-types, with some improvements to the method type definitions. astx uses ast-types to traverse code, in hopes of supporting different parsers in the future.

class Astx

import { Astx } from 'astx'

`constructor(backend: Backend, paths: NodePath<any>[] | Match[], options?: { withCaptures?: Match[] })`

backend is the parser/generator implementation being used.

paths specifies the NodePaths or Matches you want Astx methods to search/operate on.

`.find(...)` (`Astx`)

Finds matches for the given pattern within this instance's starting paths and returns an Astx instance containing the matches.

If you call astx.find('foo($$args)') on the initial instance passed to your transform function, it will find all calls to foo within the file, and return those matches in a new Astx instance.

Methods on the returned instance will operate only on the matched paths.

For example if you do astx.find('foo($$args)').find('$a + $b'), the second find call will only search for $a + $b within matches to foo($$args), rather than anywhere in the file.

You can call .find as a method or tagged template literal:

.find`pattern`
.find(pattern: string | string[] | Node | Node[] | NodePath | NodePath[] | ((wrapper: Astx) => boolean), options?: FindOptions)

If you give the pattern as a string, it must be a valid expression or statement(s). Otherwise it should be valid AST node(s) you already parsed or constructed. You can interpolate strings, AST nodes, arrays of AST nodes, and Astx instances in the tagged template literal.

For example you could do astx.find`${t.identifier('foo')} + 3`.

Or you could match multiple statements by doing

astx.find`
  const $a = $b;
  $$c;
  const $d = $a + $e;
`

This would match (for example) the statements const foo = 1; const bar = foo + 5;, with any number of statements between them.

`.closest(...)` (`Astx`)

Like .find(), but searches up the AST ancestors instead of down into descendants; finds the closest enclosing node of each input path that matches the given pattern.

`.destruct(...)` (`Astx`)

Like .find(), but doesn't test descendants of the input path(s) against the pattern; only input paths matching the pattern will be included in the result.

`FindOptions`

An object with the following optional properties:

`FindOptions.where` (`{ [captureName: string]: (path: Astx) => boolean }`)

Where conditions for node captures. For example if your find pattern is $a(), you could have { where: { $a: astx => /foo|bar/.test(astx.node.name) } }, which would only match zero-argument calls to foo or bar.

`.find(...).replace(...)` (`void`)

Finds and replaces matches for the given pattern within root.

There are several different ways you can call .replace. You can call .find in any way described above.

.find(...).replace`replacement`
.find(...).replace(replacement: string | string | Node | Node[])
.find(...).replace(replacement: (match: Astx, parse: ParsePattern) => string)
.find(...).replace(replacement: (match: Astx, parse: ParsePattern) => Node | Node[])

If you give the replacement as a string, it must be a valid expression or statement. You can give the replacement as AST node(s) you already parsed or constructed. Or you can give a replacement function, which will be called with each match and must return a string or Node | Node[] (you can use the parse tagged template string function provided as the second argument to parse code into a string. For example, you could uppercase the function names in all zero-argument function calls (foo(); bar() becomes FOO(); BAR()) with this:

astx
  .find`$fn()`
  .replace(({ captures: { $fn } }) => `${$fn.name.toUpperCase()}()`)

`.findImports(...)` (`Astx`)

A convenience version of .find() for finding imports that tolerates extra specifiers, matches value imports of the same name if type imports were requested, etc.

For example .findImports`import $a from 'a'` would match import A, { b, c } from 'a' or import { default as a } from 'a', capturing $a, whereas .find`import $a from 'a'` would not match either of these cases.

The pattern must contain only import statements.

`.addImports(...)` (`Astx`)

Like .findImports(), but adds any imports that were not found. For example given the source code:

import { foo, type bar as qux } from 'foo'
import 'g'

And the operation

const { $bar } = astx.addImports`
  import type { bar as $bar } from 'foo'
  import FooDefault from 'foo'
  import * as g from 'g'
`

The output would be

import FooDefault, { foo, type bar as qux } from 'foo'
import * as g from 'g'

With $bar capturing the identifier qux.

`.removeImports(...)` (`boolean`)

Takes import statements in the same format as .findImports() but removes all given specifiers.

`.replaceImport(...).with(...)` (`boolean`)

Replaces a single import specifier with another. For example given the input

import { Match, Route, Location } from 'react-router-dom'
import type { History } from 'history'

And operation

astx.replaceImport`
  import { Location } from 'react-router-dom'
`.with`
  import type { Location } from 'history'
`

The output would be

import { Match, Route } from 'react-router-dom'
import type { History, Location } from 'history'

The find and replace patterns must both contain a single import statement with a single specifier.

`.remove()` (`void`)

Removes the matches from .find() or focused capture(s) in this Astx instance.

`.matched` (`this | null`)

Returns this Astx instance if it has at least one match, otherwise returns null.

Since .find(), .closest(), and .destruct() always return an Astx instance, even if there were no matches, you can use .find(...).matched if you only want a defined value when there was at least one match.

`.size()` (`number`)

Returns the number of matches from the .find() or .closest() call that returned this instance.

[name: `$${string}` | `$$${string}` | `$$$${string}`] (`Astx`)

Gets an Astx instance focused on the capture(s) with the given name.

For example, you can do:

for (const { $v } of astx.find`process.env.$v`) {
  report($v.code)
}

`.placeholder` (`string | undefined`)

The name of the placeholder this instance represents. For example:

const match = astx.find`function $fn($$params) { $$body }`
console.log(match.placeholder) // undefined
const { $fn, $$params } = match
console.log($fn.placeholder) // $fn
console.log($$params.placeholder) // $$params

`.node` (`Node`)

Returns the first node of the first match. Throws an error if there are no matches.

`.path` (`NodePath`)

Returns the first path of the first match. Throws an error if there are no matches.

`.code` (`string`)

Generates code from the first node of the first match. Throws an error if there are no matches.

`.stringValue` (`string`)

Returns the string value of the first node if the focused capture is a string capture. Throws an error if there are no matches.

`[Symbol.iterator]` (`Iterator<Astx>`)

Iterates through each match, returning an Astx instance for each match.

`.matches` (`Match[]`)

Gets the matches from the .find() or .closest() call that returned this instance.

`.match` (`Match`)

Gets the first match from the .find() or .closest() call that returned this instance.

Throws an error if there were no matches.

`.paths` (`NodePath[]`)

Returns the paths that .find() and .closest() will search within. If this instance was returned by .find() or .closest(), these are the paths of nodes that matched the search pattern.

`.nodes` (`Node[]`)

Returns the nodes that .find() and .closest() will search within. If this instance was returned by .find() or .closest(), these are the nodes that matched the search pattern.

`.some(predicate)` (`boolean`)

Returns false unless predicate returns truthy for at least one match.

iteratee is function that will be called with match: Astx, index: number, parent: Astx and returns true or false.

`.every(predicate)` (`boolean`)

Returns true unelss predicate returns falsy for at least one match.

iteratee is function that will be called with match: Astx, index: number, parent: Astx and returns true or false.

`.filter(iteratee)` (`Astx`)

Filters the matches.

iteratee is function that will be called with match: Astx, index: number, parent: Astx and returns true or false. Only matches for which iteratee returns true will be included in the result.

`.map<T>(iteratee)` (`T[]`)

Maps the matches.

iteratee is function that will be called with match: Astx, index: number, parent: Astx and returns the value to include in the result array.

`.at(index)` (`Astx`)

Selects the match at the given index.

`.withCaptures(...captures)` (`Astx`)

Returns an Astx instance that contains captures from the given ...captures in addition to captures present in this instance.

You can pass the following kinds of arguments:

Astx instances - all captures from the instance will be included.
Astx[placeholder] instances - capture(s) for the given placeholder will be included.
{ $name: Astx[placeholder] } - capture(s) for the given placeholder, renamed to $name.
Match objects

Match

import { type Match } from 'astx'

`.type`

The type of match: 'node' or 'nodes'.

`.path`

The NodePath of the matched node. If type is 'nodes', this will be paths[0].

`.node`

The matched Node. If type is 'nodes', this will be nodes[0].

`.paths`

The NodePaths of the matched nodes.

`.nodes`

The matched Nodes.

`.captures`

The Nodes captured from placeholders in the match pattern. For example if the pattern was foo($bar), .captures.$bar will be the Node of the first argument.

`.pathCaptures`

The NodePaths captured from placeholders in the match pattern. For example if the pattern was foo($bar), .pathCaptures.$bar will be the NodePath of the first argument.

`.arrayCaptures`

The Node[]s captured from array placeholders in the match pattern. For example if the pattern was foo({ ...$bar }), .arrayCaptures.$bar will be the Node[]s of the object properties.

`.arrayPathCaptures`

The NodePath[]s captured from array placeholders in the match pattern. For example if the pattern was foo({ ...$bar }), .pathArrayCaptures.$bar will be the NodePath[]s of the object properties.

`.stringCaptures`

The string values captured from string placeholders in the match pattern. For example if the pattern was import foo from '$foo', stringCaptures.$foo will be the import path.

Transform files

Like jscodeshift, you can put code to perform a transform in a .ts or .js file (defaults to astx.ts or astx.js in the working directory, unless you specify a different file with the -t CLI option).

The transform file API is a bit different from jscodeshift though. You can have the following exports:

`exports.find` (optional)

A code string or AST node of the pattern to find in the files being transformed.

`exports.where` (optional)

Where conditions for capture placeholders in exports.find. See FindOptions.where ({ [captureName: string]: (path: NodePath<any>) => boolean }) for more information.

`exports.replace` (optional)

A code string, AST node, or replace function to replace matches of exports.find with.

The function arguments are the same as described in .find().replace().

`exports.astx` (optional)

A function to perform an arbitrary transform using the Astx API. It gets called with an object with the following properties:

file (string) - The path to the file being transformed
source (string) - The source code of the file being transformed
astx (Astx) - the Astx API instance
t (AstTypes) - ast-types definitions for the chosen parser
expression - tagged template literal for parsing code as an expression
statement - tagged template literal for parsing code as a statement
statements - tagged template literal for parsing code as an array of statements
report ((message: unknown) => void)
mark ((...matches: Astx[]) => void) - marks the given matches to be displayed in the matches list of vscode-astx, etc

Unlike jscodeshift, your transform function can be async, and it doesn't have to return the transformed code, but you can return a string. You can also return null to skip the file.

`exports.onReport` (optional)

If your call report(x) from an exports.astx function, this will be called with onReport({ file, report: x }).

If you are using multiple worker threads, onReport will be called in the parent process, so the report message must be a serializable value. This allows a transform to collect reports from all workers (and then potentially do something with them in finish).

If onReport returns a Promise it will be awaited.

`exports.finish` (optional)

This will be called after the transform has been run on all input files.

If you are using multiple worker threads, finish will be called in the parent process. You can use onReport and finish together to collect information from each input file and produce some kind of combined output at the end.

If finish returns a Promise it will be awaited.

Configuration

astx supports configuration in the following places (via cosmiconfig):

an astx property in package.json
an .astxrc file in JSON or YAML format
an .astxrc.json, .astxrc.yaml, .astxrc.yml, .astxrc.js, or .astxrc.cjs file
an astx.config.js or astx.config.cjs CommonJS module exporting an object

Preserving Formatting

If your codebase is formatted with prettier, I recommend trying this first:

{
  "parser": "babel/auto",
  "parserOptions": {
    "preserveFormat": "generatorHack"
  }
}

(or as CLI options)

--parser babel/auto --parserOptions '{"preserveFormat": "generatorHack"}'

If this fails you can try parser: 'recast/babel/auto' or the non-/auto parsers.

Your mileage may vary with recast; they just aren't able to keep it up to date with new syntax features in JS and TS quickly enough, and I've seen it output invalid syntax too many times.

From now on I'm going to work on a reliable solution using @babel/generator or prettier to print the modified AST, with a hook to use the original source verbatim for unmodified nodes.

Config option: `parser`

The parser to use. Options:

babel/auto (default,)
babel (faster than babel/auto, but uses default parse options instead, you may have to configure parserOptions)
recast/babel
recast/babel/auto

babel/auto automatically determines parse options from your babel config if present. babel uses fixed parse options instead, so it's faster than babel/auto, but you may have to configure parserOptions. The recast/babel(/auto) options use recast to preserve formatting. I've seen recast output invalid syntax on some files, so use with caution.

Config option: `parserOptions`

Options to pass to the parser. Right now this is just the @babel/parser options plus the following additional options:

preserveFormat (applies to: babel, babel/auto) preserveFormat: 'generatorHack' uses an experimental hack to preserve format of all unchanged nodes by hijacking internal @babel/generator API.

Config option: `prettier`

If false, don't try to use prettier to reformat transformed source code. Defaults to true.

CLI

Astx includes a CLI for performing transforms. The CLI will process the given files, then print out a diff of what will be changed, and prompt you to confirm you want to write the changes.

It will parse with babel by default using the version installed in your project and your project's babel config, if any. You can pass --parser recast/babel if you want to use recast to try to preserve formatting in the output, but I sometimes see syntax errors in its output.

Unlike jscodeshift, if prettier is installed in your project, it will format the transformed code with prettier.

Usage:

astx -f <code> [<files...>] [<directories...>]

  Searches for the -f pattern in the given files and directories
  and prints out the matches in context

astx -f <code> -r <code> [<files...>] [<directories...>]

  Quick search and replace in the given files and directories
  (make sure to quote code)

  Example:

    astx -f 'rmdir($path, $force)' -r 'rmdir($path, { force: $force })' src

astx -t <transformFile> [<files ...>] [<directories ...>]

  Applies a transform file to the given files and directories

astx [<files ...>] [<directories ...>]

  Applies the default transform file (astx.ts or astx.js in working directory)
  to the given files and directories

Options:
      --help           Show help                                       [boolean]
      --version        Show version number                             [boolean]
  -t, --transform      path to the transform file. Can be either a local path or
                       url. Defaults to ./astx.ts or ./astx.js if --find isn't
                       given
      --parser         parser to use (options: babel, babel/auto, recast/babel,
                       recast/babel/auto)                               [string]
      --parserOptions  options for parser                               [string]
  -f, --find           search pattern                                   [string]
  -r, --replace        replace pattern                                  [string]
  -y, --yes            don't ask for confirmation before writing changes
                                                                       [boolean]
      --gitignore      ignore gitignored files         [boolean] [default: true]
      --workers        number of worker threads to use                  [number]

Name		Name	Last commit message	Last commit date
Latest commit History 358 Commits
.circleci		.circleci
.vscode		.vscode
src		src
test		test
.babelrc.cjs		.babelrc.cjs
.eslintrc.cjs		.eslintrc.cjs
.gitignore		.gitignore
.mocharc.cjs		.mocharc.cjs
LICENSE.md		LICENSE.md
README.md		README.md
githooks.cjs		githooks.cjs
lint-staged.config.cjs		lint-staged.config.cjs
nyc.config.cjs		nyc.config.cjs
package.json		package.json
pnpm-lock.yaml		pnpm-lock.yaml
prettier.config.cjs		prettier.config.cjs
release.config.cjs		release.config.cjs
screenshot.png		screenshot.png
toolchain.config.cjs		toolchain.config.cjs
tsconfig.build.json		tsconfig.build.json
tsconfig.json		tsconfig.json

License

codemodsquad/astx

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astx

Table of Contents

Introduction

Usage examples

Fixing eslint errors

Restructure array concatenation

Convert require statements to imports

Combine unnecessary nested if statements

Make code DRY

Roadmap

VSCode Extension

Prior art and philosophy

Pattern Language

Placeholders

Node Placeholders ($<name>)

Array Placeholders ($$<name>)

Rest Placeholders ($$$<name>)

Anonymous Placeholders

Backreferences

Object Matching

List Matching

Ordered and unordered List Matching

Support Table

String Matching

Extracting nodes

Special Constructs

$Maybe(pattern)

$Or(...)

$And(...)

$Maybe<pattern>

$Or<...>

$And<...>

$Ordered

$Unordered

API

interface NodePath

class Astx

constructor(backend: Backend, paths: NodePath<any>[] | Match[], options?: { withCaptures?: Match[] })

.find(...) (Astx)

.closest(...) (Astx)

.destruct(...) (Astx)

FindOptions

FindOptions.where ({ [captureName: string]: (path: Astx) => boolean })

.find(...).replace(...) (void)

.findImports(...) (Astx)

.addImports(...) (Astx)

.removeImports(...) (boolean)

.replaceImport(...).with(...) (boolean)

.remove() (void)

.matched (this | null)

.size() (number)

[name: `$${string}` | `$$${string}` | `$$$${string}`] (Astx)

.placeholder (string | undefined)

.node (Node)

.path (NodePath)

.code (string)

.stringValue (string)

[Symbol.iterator] (Iterator<Astx>)

.matches (Match[])

.match (Match)

.paths (NodePath[])

.nodes (Node[])

.some(predicate) (boolean)

.every(predicate) (boolean)

.filter(iteratee) (Astx)

.map<T>(iteratee) (T[])

.at(index) (Astx)

.withCaptures(...captures) (Astx)