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JavaScript design patterns are named ways to solve recurring design problems—not a checklist every application must implement. Start with the simplest code that makes the intent clear, then add a pattern when it reduces real complexity. This guide shows when common patterns help, what they cost, and how modern JavaScript features already cover some needs older patterns addressed.
How to choose a design pattern
Before reaching for a pattern, identify the problem it is meant to solve. Compare the likely solution by how well it fits, how much indirection it adds, how it affects coupling and state ownership, how easy it is to test, and whether a native JavaScript feature already does the job.
- Use a pattern when: a recurring variation or dependency is making code harder to change, test, or understand.
- Keep the simpler version when: construction or control flow is already obvious and a pattern would add another layer without reducing complexity.
- Choose the implementation that communicates intent: JavaScript supports functional and object-oriented styles; neither requires turning every idea into a class.
Patterns are useful shared vocabulary. Learning to recognize the problem and tradeoff matters more than memorizing a catalog.
Factory: centralize choices about what to create
A factory is useful when creation depends on configuration or branching logic, while callers should use a stable interface. If creation is one uncomplicated expression, direct construction is usually clearer.
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Direct construction
function makeNotifier(channel) {
if (channel === "email") {
return { send: (message) => console.log("Email:", message) };
}
if (channel === "sms") {
return { send: (message) => console.log("SMS:", message) };
}
throw new Error(`Unsupported channel: ${channel}`);
}
const notifier = makeNotifier("email");
notifier.send("Your report is ready");This small function already acts as a factory: it hides selection and returns an object with the same send interface. A separate factory class or framework is not automatically an improvement.
When to add a more explicit factory
Centralize creation when several callers otherwise duplicate selection rules, when configuration changes which implementation is returned, or when creation itself has meaningful setup. Keep the variants behind the same call shape so consumers do not need to know which one they received. The JavaScript design-pattern book preview covers both when to use and when not to use Factory (O’Reilly preview).
Strategy: swap an algorithm without branching everywhere
Strategy represents interchangeable algorithms behind a common call shape. In JavaScript, a function parameter or a plain object dispatch table often provides enough structure; a family of strategy classes may be unnecessary.
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const prices = {
regular: (subtotal) => subtotal,
member: (subtotal) => subtotal * 0.9,
clearance: (subtotal) => subtotal * 0.7,
};
function totalFor(subtotal, pricingRule) {
return pricingRule(subtotal);
}
const total = totalFor(100, prices.member);The caller chooses the rule, while totalFor applies it without knowing how the calculation works. This is useful when algorithms vary by context or need independent testing. For a single fixed calculation, a direct expression is easier to follow. A community-maintained JavaScript pattern catalog includes Strategy; review any example code independently before reuse.
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Observer lets a subject notify callbacks when an event or state change occurs. Make registration and ownership explicit, and provide a way to unsubscribe so listeners do not outlive the component or task that needs them.
function createSubject() {
const listeners = new Set();
return {
subscribe(listener) {
listeners.add(listener);
return () => listeners.delete(listener);
},
notify(value) {
for (const listener of listeners) listener(value);
},
};
}
const progress = createSubject();
const unsubscribe = progress.subscribe((value) => {
console.log(`Progress: ${value}%`);
});
progress.notify(50);
unsubscribe();The returned cleanup function makes the subscription lifetime visible at the call site. Decide who owns the subject and who is responsible for calling cleanup; otherwise registrations can persist longer than intended.
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Observer versus a publish/subscribe event bus
Direct observer registration connects a listener to a particular subject. A publish/subscribe bus can decouple producers and consumers through named channels, but it also makes event flow less visible: a reader may need to search for publishers and subscribers across the application. Prefer direct callbacks when the relationship is local and clear; use a broader event channel only when the decoupling solves a real coordination problem.
Module: use native file boundaries first
In modern JavaScript, ES modules provide imports, exports, and file-level boundaries. Start there rather than recreating module behavior with closures and object literals. Keep internal bindings unexported and expose only the functions or values callers need.
// pricing.js
export function memberPrice(subtotal) {
return subtotal * 0.9;
}
// checkout.js
import { memberPrice } from "./pricing.js";
console.log(memberPrice(100));MDN recommends keeping imports at the top of a module, which makes dependencies easier to analyze. Whether a module specifier resolves and how files are loaded depends on the host environment and its configuration; browser and server projects may have different resolution rules. See MDN’s guides to JavaScript modules and the JavaScript language and host environment.
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Where the historical Module pattern fits
Before native modules were available, a closure could keep private variables and return an object exposing selected methods. That technique can still be useful for a small self-contained value, but it is not a prerequisite for organizing modern applications. Native module scope already provides a natural place for private bindings.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Decorator: add behavior by wrapping or composing
The Decorator pattern extends a function or object by wrapping it, leaving the original implementation usable. This can be helpful for cross-cutting behavior such as logging or timing when it is applied deliberately and does not obscure the main operation.
function withLogging(operation, log = console.log) {
return (...args) => {
log("Starting operation");
return operation(...args);
};
}
const save = (record) => ({ saved: true, record });
const saveWithLogging = withLogging(save);
saveWithLogging({ id: 7 });This example composes ordinary functions; it does not use JavaScript’s syntax-level decorators. Decorator syntax has distinct runtime and toolchain considerations, so check the implementation requirements of the environment before choosing it. The two ideas should not be conflated.
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Other patterns worth recognizing
Singleton, Proxy, Command, Dependency Injection, Mediator, and Facade are useful names for recurring approaches, but a name alone is not a reason to add an abstraction. The pattern catalog and the O’Reilly book preview document this broader vocabulary.
Singleton and shared state
A Singleton exposes one shared instance. It can be appropriate when a single instance is a genuine requirement, but it often turns dependencies into global shared state. That can make tests order-dependent and make side effects harder to trace. Prefer passing a dependency explicitly when that makes ownership and lifetime clearer.
Proxy, Command, Dependency Injection, Mediator, and Facade
- Proxy: an intermediary controls access to another object. Use it when that access control or interception is needed, not just to rename a call.
- Command: represents an operation as a value or object, useful when actions need to be queued, logged, or undone.
- Dependency Injection: supplies dependencies from outside a component, helping separate construction from use and making tests easier to configure.
- Mediator: coordinates communication among components to reduce direct links; avoid it if the central coordinator becomes harder to understand than the connections it replaces.
- Facade: presents a simpler interface over a more complex subsystem, useful when callers should not manage its internal details.
Do you need to learn design patterns for React or Node.js?
You do not need to implement a named pattern in every React or Node.js project. The practical value is recognizing the underlying problem: repeated creation branches, interchangeable behavior, event subscriptions that need cleanup, or dependencies that should be easier to replace. Then choose the lightest solution that fits the framework and runtime. Native JavaScript modules, functions, and objects often provide the needed structure without a formal pattern hierarchy.
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