---
title: "Tree Shake"
locale: "en"
version: "1.x"
canonicalUrl: "https://farmfe.org/docs/1.x/advanced/tree-shake"
publicationStatus: "prerelease"
---

<a id="tree-shake"></a>
# Tree Shake


Farm supports Tree Shake, which is automatically enabled in the default Production environment. It can be turned on or off by the [` compilation.treeShaking `](</docs/config/compilation-options#treeshaking>) option.


During Tree Shake, the ` sideEffects ` field in package.json will be automatically read, and modules with ` sideEffects ` will not perform Tree Shake.



> [!NOTE]
> note
> 
> Farm will treat all circularly dependent modules as sideEffects and will not perform Tree Shake. Please try to avoid circular dependencies in your project.



Tree shake example:


```js
import { b1, b2 } from 'b';
console.log(b1);
```


```js
export b1 = "B1";
export b2 = "B2";
```


` a.js ` is entry and it imports ` b.js `, after tree shaking, the result is:


```js
import { b1 } from 'b';
console.log(b1);
```


```js
export b1 = "B1";
```


` b2 ` is not used and will be removed in both ` a.js ` and ` b.js `


<a id="configuring-tree-shake"></a>
## Configuring Tree Shake


Tree Shake is enabled in production mode by default, to disable tree shake, use ` compilation.treeShake `:


```ts
export default {
   compilation: {
     treeShake: false,
   },
};
```


<a id="deal-with-side-effects"></a>
## Deal With Side Effects


When a module contains ` side effects `, Farm won't apply tree shake for it, and all of its imported and exports are treated as used. Farm will think following modules have ` side effects `:


1. CommonJs modules always have side effects.
2. A module contains ` self-executed ` statement at global scope has side effects
3. Modules that contains cyclic dependencies has side effects
4. Modules matches ` sideEffects ` config in its closest ` package.json `
5. Entry modules are always has side effects.


Example 1:


```js
const a = require('./')
module.exports = a;
```


CommonJs module are always has side effects.


Example 2:


```js
import a from './';

a();
```


` a() ` is executed at global scope and we treat it as side effect.


Example 3:


```js
// a.js
import b from './b.js'

// b.js
import a from './a.js'
```


` a `, ` b ` are cyclic dependencies, so they will be treated as side effects too.


Example 4:


```json
{
  "name": "my-package",
  "sideEffects": [
    "./global/**.ts"
  ]
}
```


all ts  modules under ` global/ ` are treat as side effects.