Web API

Web APIs (Application Programming Interfaces) provide built-in functionalities that allow JavaScript to interact with the browser and external services. This section covers key browser APIs, including LocalStorage, SessionStorage, Fetch API, and Geolocation API.

Local Storage and Session Storage

The Web Storage API allows storing key-value pairs in the browser.

Local Storage (Persistent Storage)

Data stored using localStorage persists even after the browser is closed.

Setting and Getting Data

// Store data
localStorage.setItem("username", "Alice");
  
// Retrieve data
let user = localStorage.getItem("username");
console.log(user); // Outputs: Alice

Removing Data

localStorage.removeItem("username"); // Removes a specific item
localStorage.clear(); // Clears all stored data

Session Storage (Temporary Storage)

Session storage works like local storage but clears data when the session (tab) is closed.

sessionStorage.setItem("sessionUser", "Bob");
console.log(sessionStorage.getItem("sessionUser"));
sessionStorage.removeItem("sessionUser");

Fetch API (Making HTTP Requests)

The Fetch API allows JavaScript to make network requests asynchronously, commonly used for retrieving data from APIs.

Fetching Data from an API

fetch("https://jsonplaceholder.typicode.com/users/1")
  .then(response => response.json()) // Convert response to JSON
  .then(data => console.log(data)) // Handle retrieved data
.catch(error => console.error("Error:", error)); // Handle errors

Using `async/await` for Fetch Requests

async function getUserData() {
  try {
    let response = await fetch("https://jsonplaceholder.typicode.com/users/1");
    let data = await response.json();
    console.log(data);
  } catch (error) {
    console.log("Error fetching data:", error);
  }
}
  
getUserData();

Sending Data Using POST Request

fetch("https://jsonplaceholder.typicode.com/posts", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({ title: "New Post", body: "Post content", userId: 1 })
})
  .then(response => response.json())
  .then(data => console.log("Post created:", data))
  .catch(error => console.log("Error:", error));

Geolocation API (Getting User Location)

The Geolocation API retrieves the user's current location.

Checking if Geolocation is Supported

if ("geolocation" in navigator) {
  console.log("Geolocation is supported!");
} else {
  console.log("Geolocation is not supported.");
}

Getting User's Current Location

navigator.geolocation.getCurrentPosition(
  position => {
    console.log("Latitude:", position.coords.latitude);
    console.log("Longitude:", position.coords.longitude);
  },
  error => console.log("Error getting location:", error.message)
);

Tracking User Location in Real-Time

navigator.geolocation.watchPosition(
  position => {
    console.log("Updated Location:", position.coords.latitude, position.coords.longitude);
  }
);

Clipboard API (Copying and Pasting Data)

The Clipboard API allows copying and pasting text programmatically.

Copying Text to Clipboard

navigator.clipboard.writeText("Copied text!").then(() => {
  console.log("Text copied to clipboard!");
});

Reading Text from Clipboard

navigator.clipboard.readText().then(text => {
  console.log("Clipboard content:", text);
});

Notification API (Displaying Browser Notifications)

The Notification API allows web applications to send notifications to users.

Requesting Notification Permission

if (Notification.permission !== "granted") {
  Notification.requestPermission().then(permission => {
    console.log("Notification permission:", permission);
  });
}

Sending a Notification

new Notification("Hello!", {
  body: "This is a notification from JavaScript.",
  icon: "icon.png"
});

Intersection Observer API (Detecting Element Visibility)

The Intersection Observer API detects when an element enters or leaves the viewport, useful for lazy loading images or triggering animations.

let observer = new IntersectionObserver(entries => {
  entries.forEach(entry => {
    if (entry.isIntersecting) {
      console.log("Element is in view:", entry.target);
    }
  });
});
  
let targetElement = document.getElementById("observe-me");
observer.observe(targetElement);

Conclusion

Web APIs extend JavaScript's capabilities by enabling data storage, making HTTP requests, accessing user location, handling clipboard interactions, and displaying notifications. The next section will explore browser compatibility and performance optimization techniques to ensure smooth execution across different devices and environments.

Forms and Input Handling

Compatibility and Performance

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