pretty-format-ast

1.0.1 verified Sat Apr 25 auth: no javascript

A plugin for pretty-format2 that prints Abstract Syntax Trees (ASTs) in a human-readable, indented format. Version 1.0.1 is the current stable release. It provides a structured view of AST nodes with their properties, types, and positions. Compared to alternatives like util.inspect, it produces a much more concise and visually organized output, specifically designed for AST inspection. The package works with any AST that follows a similar node structure and requires pretty-format2 as a peer dependency.

Common errors

error TypeError: prettyFormat2(...) is not a function ↓

cause CommonJS require of pretty-format2 may return different export depending on version. In v1.x, it is a default export function, but in v2.x, it may be exported differently.

fix

Use import: import prettyFormat2 from 'pretty-format2'; or ensure you have v1.x installed.

error Error: Cannot find module 'pretty-format2' ↓

cause pretty-format2 is a peer dependency and must be installed separately.

fix

Run: npm install pretty-format2

error SyntaxError: Unexpected token 'export' ↓

cause Using ESM imports in a CommonJS script or without proper package.json type: 'module'.

fix

Use require syntax, or set "type": "module" in package.json.

error TypeError: plugins is not iterable ↓

cause Passing a non-array value to the 'plugins' option, such as an object.

fix

Wrap the plugin in an array: plugins: [prettyFormatAST]

Warnings

gotcha Plugin must be passed as an array to the 'plugins' option. Passing a single plugin object without wrapping in an array will be silently ignored. ↓

fix Use { plugins: [prettyFormatAST] } instead of { plugins: prettyFormatAST }.

deprecated pretty-format2 v1.x is still used, but there is a newer major version v2.x. The plugin may not be compatible with v2.x without updates. ↓

fix Check compatibility with pretty-format2 v2.0.0 before upgrading.

breaking Starting from pretty-format2 v2.0.0, the plugin API changed. pretty-format-ast v1.0.1 is not updated and may not work with v2. ↓

fix Wait for an updated version of pretty-format-ast or pin pretty-format2 to v1.x.

gotcha The plugin only works with AST nodes that have a 'type' property. Objects without 'type' will not be formatted specially. ↓

fix Ensure your AST objects have a 'type' string field for proper formatting.

Install

npm install pretty-format-ast

yarn add pretty-format-ast

pnpm add pretty-format-ast

Imports

default

wrong

const prettyFormatAST = require('pretty-format-ast')

correct

import prettyFormatAST from 'pretty-format-ast'

CommonJS require works if using CJS, but ESM import is preferred for consistency.

prettyFormat2
wrong
```
const { format } = require('pretty-format2')
```
correct
```
import prettyFormat2 from 'pretty-format2'
```
prettyFormat2 is a default export; named exports like 'format' are not available.

plugins

wrong

prettyFormat2(val, { plugin: prettyFormatAST })

correct

prettyFormat2(val, { plugins: [prettyFormatAST] })

The option key is 'plugins' (plural) and must be an array.

Quickstart

Demonstrates basic usage: import pretty-format2 and pretty-format-ast, then format a simple AST object with the plugin.

const prettyFormat2 = require('pretty-format2');
const prettyFormatAST = require('pretty-format-ast');

const ast = {
  type: 'Program',
  body: [
    {
      type: 'ExpressionStatement',
      expression: { type: 'Literal', value: 42 },
    },
  ],
};

console.log(prettyFormat2(ast, { plugins: [prettyFormatAST] }));
// Output:
// Node "Program"
//   body: Array [
//     Node "ExpressionStatement"
//       expression: Node "Literal"
//         value: 42,
//   ]