# prototype-pattern

Teaches coding assistants the JavaScript Prototype Pattern. It shows how to share methods via the prototype chain to keep memory consumption low.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 614 installs · ★ 257
- Author: patterns.dev
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/PatternsDev/skills/tree/HEAD/javascript/prototype-pattern/SKILL.md
- Updated: 2026-04-15
- HTML: https://affpapa.org/en/nevibecode/skills/prototype-pattern

## What it does

This skill guides the agent on prototype-based inheritance within `**/*.js` and `**/*.ts` files. It instructs the assistant to place shared methods on prototypes rather than recreating identical functions across individual instances.

Two concrete implementation paths are detailed. The first uses standard ES6 classes, which automatically attach methods to the constructor prototype. The second relies on `Object.create()` for explicit prototype binding. The rules also cover prototype chain navigation using `extends` and `super`.

The skill strictly targets JavaScript and TypeScript file extensions. If your codebase does not instantiate multiple objects of the same shape, this pattern will offer no practical advantage.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add PatternsDev/skills --skill prototype-pattern -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/prototype-pattern/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/prototype-pattern/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add PatternsDev/skills --skill prototype-pattern -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/prototype-pattern/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add PatternsDev/skills --skill prototype-pattern -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/prototype-pattern/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install PatternsDev/skills prototype-pattern
```

2. **Manually: put the files in place**
- File: `.github/skills/prototype-pattern/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add PatternsDev/skills --skill prototype-pattern -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/PatternsDev/skills --path javascript/prototype-pattern
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/prototype-pattern/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add PatternsDev/skills --skill prototype-pattern -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/PatternsDev/skills/tree/HEAD/javascript/prototype-pattern/SKILL.md

## When to use it
- prevent function duplication across repetitive object instances
- set up explicit prototype delegation with `Object.create()`
- implement class-based prototype inheritance using `extends` and `super`
- reduce runtime memory overhead by sharing common methods

## Example prompts
- Refactor this Dog class to put common methods on the prototype chain
- Create an object inheriting from pet using Object.create instead of a class
- Review user-factory.ts to ensure methods are shared rather than copied per instance

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: b0a555045b09cd81.

BEGIN THIRD-PARTY FILE b0a555045b09cd81
````text
---
name: prototype-pattern
description: Teaches the prototype pattern for property sharing via the prototype chain. Use when creating many objects of the same type that should share methods or properties efficiently.
paths:
  - "**/*.js"
  - "**/*.ts"
license: MIT
metadata:
  author: patterns.dev
  version: "1.1"
related_skills:
  - "module-pattern"
  - "singleton-pattern"
---

# Prototype Pattern

The prototype pattern is a useful way to share properties among many objects of the same type. The prototype is an object that's native to JavaScript, and can be accessed by objects through the prototype chain.

In our applications, we often have to create many objects of the same type. A useful way of doing this is by creating multiple instances of an ES6 class.

## When to Use

- Use this when many objects need access to the same methods without duplicating them
- This is helpful for understanding JavaScript's inheritance model and ES6 classes

## Instructions

- Use ES6 classes to automatically add methods to the prototype
- Use `Object.create()` to create objects with a specific prototype
- Leverage the prototype chain for inheritance (`extends` keyword in ES6 classes)
- Understand that properties on the prototype are shared and not duplicated per instance

## Details

Let's say we want to create many dogs! In our example, dogs can't do that much: they simply have a name, and they can bark!

```js
class Dog {
  constructor(name) {
    this.name = name;
  }

  bark() {
    return `Woof!`;
  }
}

const dog1 = new Dog("Daisy");
const dog2 = new Dog("Max");
const dog3 = new Dog("Spot");
```

Notice here how the `constructor` contains a `name` property, and the class itself contains a `bark` property. When using ES6 classes, all properties that are defined on the class itself, `bark` in this case, are automatically added to the `prototype`.

We can see the `prototype` directly through accessing the `prototype` property on a constructor, or through the `__proto__` property on any _instance_.

```js
console.log(Dog.prototype);
// constructor: ƒ Dog(name, breed) bark: ƒ bark()

console.log(dog1.__proto__);
// constructor: ƒ Dog(name, breed) bark: ƒ bark()
```

The value of `__proto__` on any instance of the constructor, is a direct reference to the constructor's prototype! Whenever we try to access a property on an object that doesn't exist on the object directly, JavaScript will _go down the prototype chain_ to see if the property is available within the prototype chain.

The prototype pattern is very powerful when working with objects that should have access to the same properties. Instead of creating a duplicate of the property each time, we can simply add the property to the prototype, since all instances have access to the prototype object.

Since all instances have access to the prototype, it's easy to add properties to the prototype even after creating the instances.
````
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