AJAX XMLHttpRequest - Explained

AJAX XMLHttpRequest is a fundamental technique in web development for making asynchronous requests to the server without reloading the entire page. It allows for dynamic updating of content, improving user experience.

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1. Basic AJAX XMLHttpRequest

Using AJAX XMLHttpRequest, you can send requests to the server and handle responses asynchronously.

Example:

// Create a new XMLHttpRequest object
var xhr = new XMLHttpRequest();
// Configure the request
xhr.open('GET', 'https://api.example.com/data', true);

// Define a callback function to handle the response
xhr.onreadystatechange = function() {
if (xhr.readyState === XMLHttpRequest.DONE) {
if (xhr.status === 200) {
// Request was successful, handle response data
console.log(xhr.responseText);
} else {
// Handle errors
console.error('Error:', xhr.status);
}
}
};

// Send the request
xhr.send();

In this example, a GET request is sent to 'https://api.example.com/data'. Upon receiving a response, the callback function is executed to handle the response data.

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2. Handling Different Response Types

AJAX XMLHttpRequest supports various response types such as text, JSON, XML, and binary data.

Example:

// Request JSON data
var xhr = new XMLHttpRequest();
xhr.open('GET', 'https://api.example.com/data.json', true);
xhr.onreadystatechange = function() {
  if (xhr.readyState === XMLHttpRequest.DONE && xhr.status === 200) {
    var jsonResponse = JSON.parse(xhr.responseText);
    console.log(jsonResponse);
  }
};
xhr.send();

This example demonstrates how to request JSON data and parse the response into a JavaScript object for further manipulation.

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3. Handling POST Requests

AJAX XMLHttpRequest can also be used to send POST requests, allowing for sending data to the server.

Example:

// Send POST request with data
var xhr = new XMLHttpRequest();
xhr.open('POST', 'https://api.example.com/save', true);
xhr.setRequestHeader('Content-Type', 'application/json');
xhr.onreadystatechange = function() {
  if (xhr.readyState === XMLHttpRequest.DONE && xhr.status === 200) {
    console.log('Data saved successfully');
  }
};
var data = JSON.stringify({ username: 'john', email: 'john@example.com' });
xhr.send(data);

In this example, a POST request is sent to 'https://api.example.com/save' with JSON data containing a username and email. The server can then process this data accordingly.

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4. Error Handling

It's important to handle errors gracefully when using AJAX XMLHttpRequest to ensure a smooth user experience.

Example:

// Handle errors
var xhr = new XMLHttpRequest();
xhr.open('GET', 'https://api.example.com/invalid-endpoint', true);
xhr.onreadystatechange = function() {
  if (xhr.readyState === XMLHttpRequest.DONE) {
    if (xhr.status === 200) {
      console.log(xhr.responseText);
    } else {
      console.error('Error:', xhr.status);
    }
  }
};
xhr.send();

In this example, an error handler is included to log any errors that occur during the request.

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5. Conclusion

AJAX XMLHttpRequest is a powerful tool for making asynchronous requests in web development. By understanding its fundamentals and various scenarios, developers can create dynamic and interactive web applications.