https://github.com/preactjs/babel-plugin-transform-replace-expressions

A Babel plugin for replacing expressions with other expressions
https://github.com/preactjs/babel-plugin-transform-replace-expressions

babel babel-plugin

Last synced: 30 days ago
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A Babel plugin for replacing expressions with other expressions

• Host: GitHub
• URL: https://github.com/preactjs/babel-plugin-transform-replace-expressions
• Owner: preactjs
• License: mit
• Created: 2019-02-24T00:35:04.000Z (over 5 years ago)
• Default Branch: master
• Last Pushed: 2023-01-09T11:22:49.000Z (almost 2 years ago)
• Last Synced: 2024-04-14T05:39:52.803Z (7 months ago)
• Topics: babel, babel-plugin
• Language: JavaScript
• Homepage:
• Size: 125 KB
• Stars: 24
• Watchers: 1
• Forks: 0
• Open Issues: 1
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# babel-plugin-transform-replace-expressions ![](https://github.com/preactjs/babel-plugin-transform-replace-expressions/workflows/tests/badge.svg) [![npm](https://img.shields.io/npm/v/babel-plugin-transform-replace-expressions.svg)](https://www.npmjs.com/package/babel-plugin-transform-replace-expressions)

Replace JavaScript expressions with other expressions.

## Installation

```

$ yarn add --dev babel-plugin-transform-replace-expressions

```

## Example

Input file:

```js

const env = process.env.NODE_ENV;

typeof Hello === "number";

```

`.babelrc`:

```json

{

  "plugins": [

    [

      "babel-plugin-transform-replace-expressions",

      {

        "replace": {

          "process.env.NODE_ENV": "\"production\"",

          "typeof Hello": "42"

        }

      }

    ]

  ]

}

```

Output:

```js

const env = "production";

42 === "number";

```

## Conflict resolution

A conflict happens when two replacements have the same Babel [abstract syntax tree](https://en.wikipedia.org/wiki/Abstract_syntax_tree) representation. For example expressions `typeof A` and `typeof (A)` are formatted differently but have the same AST representation as far as the plugin is concerned. In those situations the default is to raise an error, and can be overwritten by setting the option `allowConflictingReplacements` to `true`.

You can also always give the replacements as an array of key-value pairs. When `allowConflictingReplacements` is set to `true` the _last_ conflicting replacement gets selected.

```js

{

  "plugins": [

    [

      "babel-plugin-transform-replace-expressions",

      {

        "replace": [

          ["typeof A", "B"],

          ["typeof (A)", "C"]

        ],

        "allowConflictingReplacements": true

      }

    ]

  ]

}

```

## Notes

 * Replacements are only applied to expressions. Therefore replacing `DEBUG` with `false` in `const DEBUG = true` does nothing, but for `if (DEBUG) {}` the result is `if (false) {}`.

 * Only *full* expressions count. You can't replace `env` in `process.env.NODE_ENV`, you have to replace `process.env`, which is a proper expression in Babel AST.

 * A replacement is only applied when the result is valid JavaScript. For example replacing `a` with `2` in the following code:

   ```js

   a = 1;

   b = a;

   ```

   yields

   ```js

   a = 1;

   b = 2;

   ```

## License

This plugin is licensed under the MIT license. See [LICENSE](./LICENSE).