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docs: nest mutableNamespace under cjs in stub-esm guide #2749

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12 changes: 5 additions & 7 deletions docs/guides/how-to/stub-esm.md
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Expand Up @@ -53,7 +53,7 @@ Sinon correctly raises an error here because, per the ES module spec, namespace

## The solution: use the `esm` package with `mutableNamespace`

The [`esm`](https://github.com/standard-things/esm) package is a fast, production-ready ES module loader for Node.js. It offers a `mutableNamespace` option that makes module namespace objects writable, which is what Sinon needs to install stubs.
The [`esm`](https://github.com/standard-things/esm) package is a fast, production-ready ES module loader for Node.js. It offers a `cjs.mutableNamespace` option that makes module namespace objects writable, which is what Sinon needs to install stubs.

### Step 1: Install the `esm` package

Expand All @@ -63,13 +63,12 @@ npm install --save-dev esm

### Step 2: Create a loader / setup file

Create a file at the root of your project (e.g., `esm-loader.cjs`) that enables the `mutableNamespace` option:
Create a file at the root of your project (e.g., `esm-loader.cjs`) that enables the `cjs.mutableNamespace` option:

```javascript
// esm-loader.cjs
require = require("esm")(module, {
cjs: true,
mutableNamespace: true,
cjs: { mutableNamespace: true },
});
```

Expand Down Expand Up @@ -148,8 +147,7 @@ describe("calculator", () => {

```javascript
require = require("esm")(module, {
cjs: true,
mutableNamespace: true,
cjs: { mutableNamespace: true },
});
```

Expand Down Expand Up @@ -203,7 +201,7 @@ describe("calculator", () => {

## Why does this work?

The `esm` package hooks into Node.js's module loading system. When `mutableNamespace: true` is set, it wraps ES module namespace objects with a `Proxy` that allows property assignment. Sinon's `stub()` function replaces the property on the namespace object; with the proxy in place, this assignment succeeds instead of throwing.
The `esm` package hooks into Node.js's module loading system. When `cjs.mutableNamespace` is set to `true`, it wraps ES module namespace objects with a `Proxy` that allows property assignment. Sinon's `stub()` function replaces the property on the namespace object; with the proxy in place, this assignment succeeds instead of throwing.

## Limitations and caveats

Expand Down