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https://github.com/estools/espurify

Clone AST without extra properties
https://github.com/estools/espurify

ast ecmascript estree javascript

Last synced: 6 months ago
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Clone AST without extra properties

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README 

          
espurify

================================



Clone AST without extra properties



[![Build Status][ci-image]][ci-url]

[![NPM version][npm-image]][npm-url]

[![Code Style][style-image]][style-url]

[![License][license-image]][license-url]



API

---------------------------------------



### const purifiedAstClone = espurify.purifyAst(originalAst)



Returns new clone of `originalAst` but without extra properties.



Leaves properties defined in [The ESTree Spec](https://github.com/estree/estree) (formerly known as [Mozilla SpiderMonkey Parser API](https://speakerdeck.com/michaelficarra/spidermonkey-parser-api-a-standard-for-structured-js-representations)) only. Also note that extra informations (such as `loc`, `range` and `raw`) are eliminated too.



(note: using `espurify` as a default exported function is deprecated in favor of named exports aiming ESM era, and will be removed in future major releases)



#### Supported ECMAScript versions



- [ES5](https://github.com/estree/estree/blob/master/es5.md)

- [ES2015](https://github.com/estree/estree/blob/master/es2015.md)

- [ES2016](https://github.com/estree/estree/blob/master/es2016.md)

- [ES2017](https://github.com/estree/estree/blob/master/es2017.md)

- [ES2018](https://github.com/estree/estree/blob/master/es2018.md)

- [ES2019](https://github.com/estree/estree/blob/master/es2019.md)

- [ES2020](https://github.com/estree/estree/blob/master/es2020.md)

- [ES2021](https://github.com/estree/estree/blob/master/es2021.md)

- [ES2022](https://github.com/estree/estree/blob/master/es2022.md)

- ES2023

- ES2024

- [ES2025](https://github.com/estree/estree/blob/master/es2025.md)



### const customizedCloneFunctionWithAllowList = espurify.cloneWithAllowlist(allowList)



Returns customized function for cloning AST, with user-provided `allowList`.



(note: `espurify.cloneWithWhitelist` is still exported but deprecated in favor of more inclusive language and will be removed in future major releases)



### const purifiedAstClone = customizedCloneFunctionWithAllowList(originalAst)



Returns new clone of `originalAst` by customized function.



#### allowList



| type     | default value |

|:---------|:--------------|

| `object` | N/A           |



`allowList` is an object containing NodeType as keys and properties as values.



```js

{

    ArrayExpression: ['type', 'elements'],

    ArrayPattern: ['type', 'elements'],

    ArrowFunctionExpression: ['type', 'id', 'params', 'body', 'generator', 'expression'],

    AssignmentExpression: ['type', 'operator', 'left', 'right'],

    ...

```



### const customizedCloneFunction = espurify.customize(options)



Returns customized function for cloning AST, configured by custom `options`.



### const purifiedAstClone = customizedCloneFunction(originalAst)



Returns new clone of `originalAst` by customized function.



#### options



| type     | default value |

|:---------|:--------------|

| `object` | `{}`          |



Configuration options. If not passed, default options will be used.



#### options.ecmaVersion



| type                 | default value |

|:---------------------|:--------------|

| `string` or `number` | `2025`        |



Indicates the ECMAScript version to clone. Must be either 5, 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023, 2024, 2025.



#### options.extra



| type                | default value |

|:--------------------|:--------------|

| `array` of `string` | null          |



List of extra properties to be left in result AST. For example, functions returned by `espurify.customize({extra: ['raw']})` will preserve `raw` properties of `Literal`. Functions return by `espurify.customize({extra: ['loc', 'range']})` will preserve `loc` and `range` properties of each Node.



EXAMPLE

---------------------------------------



```javascript

const espurify = require('espurify');

const estraverse = require('estraverse');

const acorn = require('acorn');

const syntax = estraverse.Syntax;

const assert = require('assert');



const jsCode = 'assert("foo")';



// Adding extra informations to AST

const originalAst = acorn.parse(jsCode, { locations: true, ranges: true, ecmaVersion: 2022 });

estraverse.replace(originalAst, {

  leave: function (currentNode, parentNode) {

    if (currentNode.type === syntax.Literal && typeof currentNode.raw !== 'undefined') {

      currentNode['x-verbatim-bar'] = {

        content : currentNode.raw,

        precedence : 18  // escodegen.Precedence.Primary

      };

      return currentNode;

    } else {

      return undefined;

    }

  }

});



// purify AST

const purifiedClone = espurify.purifyAst(originalAst);



// Extra properties are eliminated from cloned AST

assert.deepEqual(purifiedClone, {

  type: 'Program',

  body: [

    {

      type: 'ExpressionStatement',

      expression: {

        type: 'CallExpression',

        callee: {

          type: 'Identifier',

          name: 'assert'

        },

        arguments: [

          {

            type: 'Literal',

            value: 'foo'

          }

        ],

        optional: false

      }

    }

  ],

  sourceType: 'script'

});



// original AST is not modified

assert.deepEqual(originalAst,{

  type: 'Program',

  start: 0,

  end: 13,

  loc: {

    start: {

      line: 1,

      column: 0

    },

    end: {

      line: 1,

      column: 13

    }

  },

  range: [

    0,

    13

  ],

  body: [

    {

      type: 'ExpressionStatement',

      start: 0,

      end: 13,

      loc: {

        start: {

          line: 1,

          column: 0

        },

        end: {

          line: 1,

          column: 13

        }

      },

      range: [

        0,

        13

      ],

      expression: {

        type: 'CallExpression',

        start: 0,

        end: 13,

        loc: {

          start: {

            line: 1,

            column: 0

          },

          end: {

            line: 1,

            column: 13

          }

        },

        range: [

          0,

          13

        ],

        callee: {

          type: 'Identifier',

          start: 0,

          end: 6,

          loc: {

            start: {

              line: 1,

              column: 0

            },

            end: {

              line: 1,

              column: 6

            }

          },

          range: [

            0,

            6

          ],

          name: 'assert'

        },

        arguments: [

          {

            type: 'Literal',

            start: 7,

            end: 12,

            loc: {

              start: {

                line: 1,

                column: 7

              },

              end: {

                line: 1,

                column: 12

              }

            },

            range: [

              7,

              12

            ],

            value: 'foo',

            raw: '"foo"',

            "x-verbatim-bar": {

              content: '"foo"',

              precedence: 18

            }

          }

        ],

        optional: false

      }

    }

  ],

  sourceType: 'script'

});

```



INSTALL

---------------------------------------



### via npm



Install



    $ npm install --save espurify



Use



```javascript

const espurify = require('espurify');

```



AUTHOR

---------------------------------------

* [Takuto Wada](https://github.com/twada)



CONTRIBUTORS

---------------------------------------

* [Renée Kooi](https://github.com/goto-bus-stop)

* [Andreas Lind](https://github.com/papandreou)



LICENSE

---------------------------------------

Licensed under the [MIT](https://github.com/estools/espurify/blob/master/MIT-LICENSE.txt) license.



[npm-url]: https://npmjs.org/package/espurify

[npm-image]: https://badge.fury.io/js/espurify.svg



[ci-image]: https://github.com/estools/espurify/workflows/Node.js%20CI/badge.svg

[ci-url]: https://github.com/estools/espurify/actions?query=workflow%3A%22Node.js+CI%22



[style-url]: https://github.com/Flet/semistandard

[style-image]: https://img.shields.io/badge/code%20style-semistandard-brightgreen.svg



[license-url]: https://github.com/estools/espurify/blob/master/MIT-LICENSE.txt

[license-image]: https://img.shields.io/badge/license-MIT-brightgreen.svg