#Non Promise Based APIs

1. 1. They are synchronous APIs that do not return promises.
2. 2. Types of Non Promise Based APIs :
   • setTimeout
   • setInterval
   • requestAnimationFrame
   • XMLHttpRequest
   • Web Storage API
3. 3. setTimeout
   • Used to execute a function once after a specified delay.
   • Delay is in milliseconds (1000ms = 1 second).
   • It returns a unique identifier (timeoutId).
   • Function execution can be cancelled using clearTimeout(timeoutId).
   • Syntax:setTimeout(callback, delayInMilliseconds, param1, param2, ...)
   • Example:
     1// Example 1: Basic setTimeout
     2setTimeout(() => {
     3  console.log("Hello after 2 seconds");
     4}, 2000);
     5
     6// Example 2: With parameters
     7setTimeout((name) => {
     8  console.log(`Hello ${name}!`);
     9}, 1000, "John");
     10
     11// Example 3: Cancelling timeout
     12const timeoutId = setTimeout(() => {
     13  console.log("This will never run");
     14}, 1000);
     15
     16clearTimeout(timeoutId); // Cancels the timeout

4. 4. setInterval
   • Used to repeatedly execute a function at fixed time intervals.
   • Interval is in milliseconds (1000ms = 1 second).
   • It returns a unique identifier (intervalId) that can be used to stop the interval.
   • Function execution can be cancelled using clearInterval(intervalId).
   • Continues until clearInterval is called.
   • Syntax:setInterval(callback, intervalInMilliseconds, param1, param2, ...)
   • Example:
     1// Example 1: Basic counter
     2let count = 0;
     3const intervalId = setInterval(() => {
     4  count++;
     5  console.log(`Count: ${count}`);
     6  if(count >= 5) {
     7    clearInterval(intervalId);
     8  }
     9}, 1000);
     10
     11// Example 2: With parameters
     12let score = 0;
     13const gameInterval = setInterval((points) => {
     14  score += points;
     15  console.log(`Score: ${score}`);
     16}, 1000, 10);
     17
     18// Stop after 5 seconds
     19setTimeout(() => {
     20  clearInterval(gameInterval);
     21  console.log("Game Over!");
     22}, 5000);

5. 5. requestAnimationFrame
   • Used for smooth animations and visual updates.
   • Executes before the browser's next repaint.
   • Better for animations than setInterval (smoother, battery-friendly).
   • Syntax:requestAnimationFrame(callback)
   • Example:
     1// Example: Simple animation
     2let position = 0;
     3let animationId;
     4
     5function moveBox() {
     6  position += 2;
     7  box.style.left = position + 'px';
     8  
     9  if(position < 300) {
     10    // Continue animation
     11    animationId = requestAnimationFrame(moveBox);
     12  }
     13}
     14
     15// Start animation
     16animationId = requestAnimationFrame(moveBox);
     17
     18// Stop animation (if needed)
     19cancelAnimationFrame(animationId);

6. 6. XMLHttpRequest
   • Old way to make HTTP requests (before fetch).
   • Uses events to handle responses.
   • Can be synchronous or asynchronous.
   • Syntax:const xhr = new XMLHttpRequest()
   • Example:
     1// Example: Making a GET request
     2const xhr = new XMLHttpRequest();
     3
     4// Setup request handlers
     5xhr.onreadystatechange = function() {
     6  if(xhr.readyState === 4) { // Request completed
     7    if(xhr.status === 200) { // Success
     8      console.log('Data:', xhr.responseText);
     9    } else {
     10      console.error('Error:', xhr.status);
     11    }
     12  }
     13};
     14
     15// Open and send request
     16xhr.open("GET", "https://api.example.com/data", true);
     17xhr.send();

7. 7. Web Storage API
   • Used to store data in the browser.
   • localStorage: persists even after browser closes.
   • sessionStorage: cleared when browser session ends.
   • Syntax:localStorage.setItem(key, value)sessionStorage.setItem(key, value)
   • Example:
     1// Example 1: Using localStorage
     2// Store data
     3localStorage.setItem('username', 'john_doe');
     4localStorage.setItem('isLoggedIn', 'true');
     5
     6// Get data
     7const username = localStorage.getItem('username');
     8console.log(username); // 'john_doe'
     9
     10// Remove specific item
     11localStorage.removeItem('isLoggedIn');
     12
     13// Clear all data
     14localStorage.clear();
     15
     16// Example 2: Using sessionStorage
     17sessionStorage.setItem('tempData', 'some value');
     18const data = sessionStorage.getItem('tempData');
     19sessionStorage.removeItem('tempData');

8. 8.
   Important Notes:

   • These APIs are older but still widely used.
   • Modern alternatives like Promises and fetch API are often preferred.
   • Web Storage API only stores strings (use JSON.stringify for objects).
   • Always clean up intervals and timeouts to prevent memory leaks.