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abstract syntax tree class for js

Package Exports

  • abstract-syntax-tree

This package does not declare an exports field, so the exports above have been automatically detected and optimized by JSPM instead. If any package subpath is missing, it is recommended to post an issue to the original package (abstract-syntax-tree) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

abstract-syntax-tree

npm Build Status

What is an abstract syntax tree?

An abstract syntax tree is a way to represent the source code. In case of this library it is represented in the estree format.

For example, the following source code:

const answer = 42

Has the following representation:

{
  "type": "Program",
  "body": [
    {
      "type": "VariableDeclaration",
      "declarations": [
        {
          "type": "VariableDeclarator",
          "id": {
            "type": "Identifier",
            "name": "answer"
          },
          "init": {
            "type": "Literal",
            "value": 42
          }
        }
      ],
      "kind": "const"
    }
  ]
}

What are abstract syntax trees used for?

They're used e.g. for code's:

  • highligthing
  • linting
  • refactoring
  • transformations
  • analysis
  • minification
  • obfuscation
  • generation
  • source maps

Installation

npm install abstract-syntax-tree

Key Features

  • source to ast conversion
  • ast to source generation
  • ast traversal
  • ast manipulation

Methods

find

Find all nodes of given type.

const source = 'const a = "x";'
const ast = new AbstractSyntaxTree(source)
ast.find('VariableDeclaration')

each

Iterate over all nodes of given type.

const source = 'const a = "x";'
const ast = new AbstractSyntaxTree(source)
ast.each('VariableDeclaration', node => {})

has

Check if ast contains a node of given type.

const source = 'const a = "x";'
const ast = new AbstractSyntaxTree(source)
ast.has('VariableDeclaration')

count

Count ast nodes of given type.

const source = 'const a = "x"; const b = "y";'
const ast = new AbstractSyntaxTree(source)
ast.count('VariableDeclaration')

first

First first node of given type.

const source = 'var a = "x";'
const ast = new AbstractSyntaxTree(source)
ast.first('VariableDeclaration')

last

Find last node of given type.

const source = 'const a = "x";'
const ast = new AbstractSyntaxTree(source)
ast.last('VariableDeclaration')

remove

Remove all nodes that match the criteria.

const source = '"use strict"; const b = 4;'
const ast = new AbstractSyntaxTree(source)
ast.remove({ type: 'Literal', value: 'use strict' })
const source = 'function hello () { const foo = "bar"; return "world"; }'
const ast = new AbstractSyntaxTree(source)
ast.remove('BlockStatement > VariableDeclaration')

walk

Walks over all nodes

const source = 'const a = 1'
const ast = new AbstractSyntaxTree(source)
ast.walk((node, parent) => {})

traverse

Walks over all nodes

const source = 'const a = 1'
const ast = new AbstractSyntaxTree(source)
ast.walk({
  enter (node) {},
  leave (node) {}
})

replace

Replace all nodes that match the criteria.

const source = 'const a = 1'
const ast = new AbstractSyntaxTree(source)
ast.replace({
  enter (node) {
    if (node.type === 'VariableDeclaration') {
      node.kind = 'let'
    }
    return node
  }
})

prepend

Prepend a node to the body.

const source = 'const a = 1;'
const ast = new AbstractSyntaxTree(source)
ast.prepend({
  type: 'ExpressionStatement',
  expression: {
    type: 'Literal',
    value: 'use strict'
  }
})

append

Append a node to the body.

const source = 'const a = 1;'
const ast = new AbstractSyntaxTree(source)
ast.append({
  type: 'ExpressionStatement',
  expression: {
    type: 'Literal',
    value: 'test'
  }
})

wrap

Wrap body with given node.

const source = 'const a = 1;'
const ast = new AbstractSyntaxTree(source)
ast.wrap(body => {
    return [
      {
        type: 'ExpressionStatement',
        expression: {
          type: 'CallExpression',
          callee: {
            type: 'FunctionExpression',
            params: [],
            body: {
              type: 'BlockStatement',
              body
            }
          },
          arguments: []
        }
      }
    ]
})

unwrap

Change the code to the first BlockStatement body

const source = '(function () { console.log(1); }())'
const ast = new AbstractSyntaxTree(source)
ast.unwrap()
ast.toSource()

template

Create ast partials from templates

const source = 'console.log(1);'
const ast = new AbstractSyntaxTree(source)
ast.template('const foo = <%= bar %>;' { bar: { type: 'Literal', value: 1 } })

mark

Add cid to all nodes

const ast = new AbstractSyntaxTree('const a = 1;')
ast.mark()
assert(ast.first('Program').cid === 1)
assert(ast.first('VariableDeclaration').cid === 2)

toSource

Convert the ast to string.

const source = 'const a = 1;'
const ast = new AbstractSyntaxTree(source)
const source = ast.toSource()
const source = 'const a = 1;'
const ast = new AbstractSyntaxTree(source)
const { source, map } = ast.toSource({ sourceMap: true })

toSourceMap

Generates a source map.

const source = 'const a = 1;'
const ast = new AbstractSyntaxTree(source)
const map = ast.toSourceMap()