Episode 7:Understanding Hoisting in Yarn Workspaces

What Is Hoisting?

Hoisting in Yarn Workspaces refers to the process of lifting dependencies from individual package directories to a shared node_modules folder at the root of the repository.

This mechanism optimizes:

1. Dependency Management:

   • Avoids duplicate installations for shared dependencies.

2. File System Structure:

   • Simplifies the node_modules layout for better performance and disk usage.

3. Package Linking:

   • Ensures packages are symlinked efficiently.

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How Hoisting Works

1. Workspace Package Symlinks:

   • Symlinks for workspace packages (e.g., moduleA and moduleB) are hoisted to the root node_modules folder.

   • This allows a single symlink per package, resolving dependencies globally.

2. Shared Dependencies:

   • Dependencies installed for one module but required by others are hoisted to the root node_modules.

   • Example: Installing lodash for both moduleA and moduleB results in one shared copy at the root.

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Practical Example: Hoisting in Action

1. Checking Node Modules

In a typical Yarn Workspace setup:

• moduleA/node_modules/ → No folder present.

• moduleB/node_modules/ → No folder present.

• root/node_modules/ → Contains symlinks for moduleA, moduleB, and shared dependencies.

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2. Installing Shared Dependencies

Step 1: Install lodash in moduleA

Run:

yarn workspace moduleA add lodash

Check the root node_modules:

• lodash/ → Installed here, shared globally.

Step 2: Install lodash in moduleB

Run:

yarn workspace moduleB add lodash

Since lodash is already hoisted to the root, no additional copy is created. Both moduleA and moduleB access the same instance.

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3. Handling Version Conflicts

If two modules require different versions of the same dependency:

1. Root Version:

   • The version required by one module (e.g., lodash@4.17.21) is installed at the root.

2. Per-Module Version:

   • The conflicting version (e.g., lodash@3.10.1) is installed in the node_modules folder of the module that needs it.

Example:

• root/node_modules/lodash/ → 4.17.21

• packages/moduleB/node_modules/lodash/ → 3.10.1

Each module will resolve the correct version via Node’s module resolution algorithm.

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No-Hoist Dependencies

When to Use nohoist

Some packages are not compatible with hoisting, such as:

• React Native

• Electron

• Packages with binaries or non-JavaScript files that depend on specific locations.

Defining nohoist

You can specify packages that shouldn’t be hoisted in the root package.json under the workspaces property:

{
  "workspaces": {
    "packages": ["packages/*"],
    "nohoist": [
      "**/react-native",
      "**/react-native/**"
    ]
  }
}

Effect of nohoist

• react-native and its dependencies will be installed locally within each package’s node_modules.

• These dependencies will not appear in the root node_modules.

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Benefits of Hoisting

1. Efficiency:

   • Reduces disk usage by avoiding duplicate installations.

2. Performance:

   • Improves dependency resolution speed due to centralized management.

3. Flexibility:

   • Handles version conflicts seamlessly when needed.

4. Compatibility:

   • Allows opting out for specific packages via nohoist.

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Summary

• Hoisting centralizes shared dependencies at the root of a Yarn Workspace project, optimizing performance and disk usage.

• Yarn resolves conflicts by installing specific versions in individual package directories when needed.

• Use the nohoist option for packages that cannot or should not be hoisted.

Yarn Workspaces with hoisting provide a clean, efficient, and scalable solution for managing monorepos. 🎉