VueJS

The key features of Vue include:

• Declarative Rendering: Vue extends standardHTML with a template syntax that allows you to describe HTML output based on JavaScript state
• Reactivity: Vue automatically tracksJavaScript state changes and efficiently updates the DOM when changes happen.
• Component-Based Architecture: Applications are built using small, self-contained, and reusable components
• Directives: Special attributes starting with v-if, v-for, and v-bind that apply reactive behavior to the DOM.
• Virtual DOM: Vue uses a Virtual DOM to minimize actual DOM manipulations, improving performance.

• Gentle Learning Curve: If you know HTML, CSS,and JavaScript, you can start building with Vue quickly.
• Versatility: It can be used as a simple library to enhance static HTML or as a full-featured framework for complex SPAs.
• High Performance: Its lightweight nature and optimized re-rendering make it very fast.
• Great Documentation: Vue is famous in the dev community for having exceptionally clear and thorough official documentation.

As of January 2026, the latest stable version of Vue is 3.5.x. Vue 3 is the current industry standard, having replaced Vue 2 (which reached end-of-life in late 2023).

For modern development, the recommended way to start a Vue project is usingVite.

1. Run the creator tool: Open your terminal and run: npm create vue@latest
2. Follow the prompts: Enter your project name and select features (like TypeScript or Vue Router).
3. Install & Run:

• Options API: The traditional way where you define logic using an object of options like data, methods,and mounted. Best for smaller components.
• Composition API: Introduced in Vue 3, it uses the setup attribute or function to group logic by logical concern rather than option type. It is better for large-scale applications and reusability.

Directives are special tokens in the markup that tell the library to do something to a DOM element.

• v-bind: Dynamically binds an attribute (e.g.,:src="imagePath")
• v-model: Creates two-way data binding on form inputs
• v-if / v-else: Conditionally renders an element
• v-for: Renders a list of items by looping through an array

A Single-File Component is a file with a .vue extension that encapsulates the structure (HTML), logic (JavaScript), and styling (CSS) of a component in one place. Example (MyComponent.vue):

In large applications, passing data between many nested components becomes difficult. State management libraries provide a "central store" for all components.

• Pinia: The current officially recommended state management library for Vue 3. It is lightweight and has excellent TypeScript support.
• Vuex: The older state management library used primarily in Vue 2 projects.

Lifecycle hooks are built-in functions that allow you to execute code at specific stages of a component's existence, such as when it is created, added to the DOM, or destroyed.

• onMounted(): Called after the component has been mounted.
• onUpdated(): Called after the component has updated its DOM tree due to a state change.
• onUnmounted(): Called after the component has been removed.

Vue Router is the official router for Vue.js. It syncs the browser's URL with Vue's components, allowing you to build Single-Page Applications where the page doesn't refresh when the user navigates to different sections (like /about or /profile).

Both v-if and v-show are used to conditionally display elements in Vue.js. However, they differ significantly in how they handle the DOM and when they should be used for performance optimization.

Comparison Table

The v-for directive is used to render a list of items based on an array or an object. It uses a specific syntax: item in items, where items is the source data and item is an alias for the element being iterated.

• Iterating Arrays: You can access the element and its index: v-for="(item, index) in items".
• Iterating Objects: You can iterate through properties: v-for="(value, key, index) in myObject".
• Range Support: It can also take an integer to repeat a template a fixed number of times: v-for="n in 10".

The Role of the :key Attribute
The :key attribute is a unique identifier used by Vue’s Virtual DOM algorithm to identify nodes when updating the list. Without keys, Vue uses an "in-place patch" strategy, which can lead to UI bugs.

Implementation Example

In the Composition API, both ref and reactive are used to create reactive state. While they achieve similar goals, they handle data types and access patterns differently.

Computed Properties Overview

Computed properties are reactive functions that allow you to describe a value that depends on other data properties. They are "derived" state—when the source data changes, the computed property automatically re-evaluates and updates.

Key Differences: Computed vs. Methods

The primary difference is caching. Computed properties cache their results based on their reactive dependencies, whereas methods execute every time they are called.

Technical Breakdown

• 1. The Power of Caching: If you have a computed property that filters a massive list, and that list hasn't changed, Vue will return the previously calculated result instantly. A method would force Vue to re-filter the entire list every time any unrelated part of the page updates.
• 2. Dependency Tracking: Vue's reactivity system tracks which variables are used inside a computed property. If computedValue depends on firstName and lastName, it will only run again if one of those two variables changes.

Best Practices

• Computed for Templates: Always use computed properties for complex logic inside your HTML to keep templates clean and readable.
• Avoid Side Effects: Never try to change other data properties or make asynchronous calls (like fetch) inside a computed property; use Watchers for those tasks.
• Getters and Setters: By default, computed properties are "getter-only," but you can provide a "setter" if you need to manually update the source data when the computed value is changed.

Implementation Example

Watchers Overview

In Vue.js, Watchers allow you to perform "side effects" in response to state changes. Unlike computed properties, which are used to derive new data, watchers are used for asynchronous operations, DOM manipulation, or changing other pieces of state when a specific dependency changes.

Comparison: watch vs. watchEffect

Vue 3 provides two main ways to watch data. While they share a similar goal, they differ in how they track dependencies and when they run for the first time.

Key Concepts and Features

• Deep Watching: By default, watch is shallow. If you want to watch nested properties inside an object, you must set the { deep: true } option.
• Immediate Execution: You can make a watch run immediately on setup (like watchEffect) by passing { immediate: true }.
• Cleanup Side Effects: Both functions allow you to define a cleanup callback (e.g., to cancel an API request or clear a timer) that runs right before the effect re-runs or when the component is unmounted.
• Flush Timing: You can control whether the watcher runs before or after Vue updates the DOM using the flush option ('pre', 'post', or 'sync').

Practical Examples

When to use Watchers vs. Computed

• Computed: Use for transforming data to be displayed in the template (Pure functions).
• Watchers: Use for Side Effects such as API calls, logging, changing the URL, or manual DOM updates.

Two-Way Data Binding Overview

In Vue.js, two-way data binding refers to the synchronization between the user interface (View) and the underlying data (Model). When the data changes, the UI updates; conversely, when the user interacts with the UI (e.g., typing in an input), the data updates automatically.

The v-model directive is the primary tool used to achieve this. It acts as "syntactic sugar," combining property binding and event listening into a single attribute.

How v-model Works Internally

While v-model looks like a single operation, it is actually a shorthand for two separate actions:

1. Binding a value: It passes a data property to the element (typically via the value attribute).
2. Listening for changes: It listens for an input event and updates the data property with the new value.

Key Features and Modifiers

Vue provides built-in modifiers to change how v-model behaves during user interaction:

• .lazy: Instead of updating the data on every keystroke (input event), it only updates when the user leaves the input field (change event).
• .number: Automatically casts the user input string into a valid JavaScript number.
• .trim: Automatically strips whitespace from the beginning and end of the user input.

Using v-model with Components

In Vue 3, v-model is highly flexible when used on custom components:

• Default usage: Uses a prop named modelValue and emits an event named update:modelValue.
• Multiple v-models: You can bind multiple data points to a single component by specifying an argument (e.g., v-model:firstName="name" and v-model:lastName="surname").

Implementation Comparison

Passing Data with Props

In Vue.js, data flows downward from parent components to child components using Props. Props are custom attributes you register on a component; when a value is passed to a prop attribute, it becomes a property on that component instance.

Key Characteristics of Props

• One-Way Data Flow: Data flows down, but not up. If the parent updates the prop, the child updates automatically. However, the child must not attempt to mutate a prop directly.
• Reactive: Props are reactive; if the parent's data changes, the child will reflect those changes immediately.
• Type Safety: You can define the expected data type (String, Number, Object, etc.) to ensure the component is used correctly.

Implementation Steps

Code Example

Prop Validation Rules

It is a best practice to provide requirements for your props. If the requirements are not met, Vue will warn you in the browser console.

• Type: String, Number, Boolean, Array, Object, Date, Function, Symbol.
• Required: { required: true }.
• Default: { default: 'Hello' } or a factory function for objects/arrays.
• Validator: A custom function to validate the value logic.

Emitting Events Overview

In Vue.js, while Props allow a parent to send data down, Emits allow a child to send messages or data back up to the parent. This follows the core design pattern: "Props down, Events up".

When a child component triggers an event using $emit, the parent component can listen for that specific event and execute a method or update its own state in response.

Implementation Steps

Detailed Code Example

Key Rules and Best Practices

• Kebab-case for Listeners: While you can use camelCase in JavaScript, Vue recommends using kebab-case in the HTML template (e.g., @update-value).
• Validation: You can validate emits in Vue 3 by passing an object to defineEmits that checks if the payload is valid before sending it.
• One-Way Data Flow: Never change a prop inside the child to communicate with the parent; always emit an event so the parent can change its own state.
• Multiple Arguments: You can pass multiple arguments as a payload: emit('update', arg1, arg2).

Teleport Overview

Teleport is a built-in component in Vue 3 that allows you to "transport" a piece of a component's template to a different part of the DOM tree, outside of the component's hierarchical structure.

Even though the element is rendered in a different location (like the <body> or a specific #container div), it still behaves like a normal child of the original component—meaning it can access the component's state, props, and scoped styles.

Why is Teleport Necessary?

In standard Vue development, components are rendered within their parents. However, certain UI elements can be broken by CSS properties like z-index, overflow: hidden, or position: relative in the parent container.

How to Use Teleport

The <Teleport> component requires a to target, which can be a CSS selector string (like an ID or class) or an actual DOM element.

Key Features and Behaviors

• Logical vs. Physical: It remains a logical child of the component. You can pass props to it and emit events from it as if it hadn't moved.
• Disabled State: You can toggle the teleportation using the :disabled prop. When disabled, the content stays inside the original component structure.
• Multiple Teleports: Multiple <Teleport> components can send content to the same target element. They will simply be appended one after another.
• Scoped CSS: Styles defined in <style scoped> will still apply to the teleported content because it remains part of the virtual component tree.

Slots are a powerful distribution mechanism in Vue.js that allow a parent component to inject HTML, components, or plain text into a child component’s template. This makes components highly reusable by allowing the parent to define the "content" while the child defines the "layout".

Types of Slots

Understanding Scoped Slots

Normally, a parent cannot access data inside a child's scope. Scoped Slots bridge this gap by allowing the child to "provide" data to the slot's content in the parent.

The Workflow:

1. Child: Defines a <slot> and binds data to it using attributes (props).
2. Parent: Receives that data via the v-slot directive value.

Implementation Example

Child Component (UserList.vue):
The child iterates through data but lets the parent decide how to display each item.

Parent Component:
The parent accesses the userData via the #item slot.

Key Benefits of Scoped Slots

• Inversion of Control: The child manages the logic (fetching, filtering, or looping), while the parent manages the visual representation.
• Flexibility: You can use the same component for a "Card View" in one part of your app and a "Table View" in another, just by changing the slot template.
• Encapsulation: Keeps the child component focused on data/state management without hardcoding UI styles.

KeepAlive Overview

<KeepAlive> is a built-in component in Vue that caches component instances when they are dynamically toggled.

Normally, when a component is switched out (e.g., via v-if or <component :is="...">), it is destroyed and its state is lost. Wrapping these components in <KeepAlive> preserves their state and avoids the performance overhead of re-creating the DOM and re-fetching data.

Key Behaviors and Lifecycle

When a component is cached by <KeepAlive>, its standard lifecycle hooks behave differently, and two specialized hooks are introduced:

Core Properties

You can control which components are cached using the following props:

• include: Only components with matching names will be cached (String, Regex, or Array).
• exclude: Any component with a matching name will not be cached.
• max: Limits the maximum number of component instances to cache. When the limit is reached, the least recently used (LRU) instance is destroyed.

Common Use Cases

Implementation Example

Asynchronous Components Overview

In large applications, loading every component at once can lead to a massive initial JavaScript bundle, causing slow page loads. Asynchronous Components allow you to split your app into smaller chunks and load components from the server only when they are actually needed.

In Vue 3, this is achieved using the defineAsyncComponent function.

Implementation Approaches

Basic vs. Advanced Syntax

The most common way to lazy-load a component:

For a better user experience, you can manage the "waiting" period:

Key Benefits

• Code Splitting: Build tools like Vite or Webpack automatically recognize dynamic imports and create separate .js files for them.
• Reduced Initial Load: Users only download the code for the page they are currently visiting.
• Improved Performance: Smaller entry bundles lead to faster "Time to Interactive" (TTI).

Using with <Suspense>

Vue 3's <Suspense> component can coordinate the loading state of an entire tree of async components. It provides "slots" for the ready state and the loading (fallback) state.

Provide and Inject Overview

Provide and Inject is a feature in Vue used for dependency injection. It allows a "grandparent" or ancestor component to serve as a dependency provider for all its descendants, regardless of how deep the component hierarchy is.

This solves the problem of "Prop Drilling," where data must be passed through multiple layers of intermediate components that don't actually need the data themselves.

How It Works

Provide/Inject vs. Props

Implementation Example

Best Practices

• Reactivity: To keep the injected data reactive, ensure you provide a ref or reactive object.
• Symbol Keys: For large applications, use Symbols as keys instead of strings to avoid naming collisions between different plugins or components.
• Mutations: If a child needs to change the data, it is best practice to provide a function (like toggleTheme) that performs the mutation in the ancestor, rather than letting the child mutate state directly.
• Plugin Usage: This pattern is the primary way Vue plugins (like Vue Router or Pinia) make their instances available to your entire app.

Component Registration Overview

In Vue.js, you must register components so that Vue knows how to locate and render them when they are used in a template. There are two primary ways to do this: Global and Local registration.

Comparison Table

Implementation Differences

Registered in the main entry file (usually main.js). Once registered, you do not need to import them again in any .vue file.

The component is imported and used only where it is needed. This is the recommended approach for most components.

Pros and Cons