### Install Defu with Yarn, NPM, or PNPM

Source: https://github.com/unjs/defu/blob/main/README.md

Install the defu package using your preferred package manager.

```bash
# yarn
yarn add defu
# npm
npm install defu
# pnpm
pnpm install defu
```

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

### Defu Example: Merging Objects

Source: https://github.com/unjs/defu/blob/main/README.md

Demonstrates how `defu` merges nested objects, preserving existing properties and adding new ones from defaults.

```javascript
import { defu } from "defu";

console.log(defu({ a: { b: 2 } }, { a: { b: 1, c: 3 } }));
// => { a: { b: 2, c: 3 } }
```

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

### Defu Array Concatenation Example

Source: https://github.com/unjs/defu/blob/main/README.md

Demonstrates how `defu` concatenates array values when a default property is defined.

```javascript
console.log(defu({ array: ["b", "c"] }, { array: ["a"] }));
// => { array: ['b', 'c', 'a'] }
```

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

### Create Custom Defu Merger

Source: https://github.com/unjs/defu/blob/main/README.md

Use `createDefu` to instantiate a custom merger function. This example shows summing numbers instead of overriding them.

```javascript
import { createDefu } from "defu";

const ext = createDefu((obj, key, value) => {
  if (typeof obj[key] === "number" && typeof value === "number") {
    obj[key] += value;
    return true;
  }
});

ext({ cost: 15 }, { cost: 10 }); // { cost: 25 }
```

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

### Defu Type Utility Example

Source: https://github.com/unjs/defu/blob/main/README.md

Utilize the `Defu` type utility to infer the merged TypeScript type of objects with default values.

```typescript
import type { Defu } from 'defu'

type Options = Defu<{ foo: 'bar' }, [{}, { bar: 'baz' }, { something: 42 }]>
// returns { foo: 'bar', bar: 'baz', 'something': 42 }
```

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

### Basic Defu Usage

Source: https://github.com/unjs/defu/blob/main/README.md

Import and use the `defu` function to assign default properties recursively. Leftmost arguments have higher priority.

```javascript
import { defu } from "defu";

const options = defu(object, ...defaults);
```

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

### Using Defu with CommonJS

Source: https://github.com/unjs/defu/blob/main/README.md

Import the `defu` function when using CommonJS modules.

```javascript
const { defu } = require("defu");
```

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

### Defu with Function Merger

Source: https://github.com/unjs/defu/blob/main/README.md

Utilize `defuFn` to allow functions as default values, which are then called with the default value. Useful for manipulating defaults.

```javascript
import { defuFn } from "defu";

defuFn(
  {
    ignore: (val) => val.filter((item) => item !== "dist"),
    count: (count) => count + 20,
  },
  {
    ignore: ["node_modules", "dist"],
    count: 10,
  },
);
/*
 { 
    ignore: ['node_modules'],
    count: 30
  }
  */
```

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

### Defu with Array Function Merger

Source: https://github.com/unjs/defu/blob/main/README.md

Use `defuArrayFn` for function mergers that specifically apply only to array values defined in defaults.

```javascript
import { defuArrayFn } from "defu";

defuArrayFn(
  {
    ignore: (val) => val.filter((i) => i !== "dist"),
    count: () => 20,
  },
  {
    ignore: ["node_modules", "dist"],
    count: 10,
  },
);
/*
  {
    ignore: ['node_modules'],
    count: () => 20
  }
  */
```

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