Web Storage API

Web developers may use the Web Storage API, a collection of JavaScript APIs, to save information locally inside a user’s web browser. The Web Storage API offers two distinct data-archival options:

Using local storage, we may save data (keys and values) in the user’s browser that will remain there even after the user closes the browser. This implies that the web app can still access the user’s data even after they’ve navigated away from the page.

This feature, known as “session storage,” allows for the temporary storage of key/value pairs in a user’s web browser. When the user exits the web application or shuts their browser, any data saved in Session Storage will be deleted.

The Web Storage API is helpful for keeping track of the little bits of information that a web app needs, such user preferences, session data, and application settings. It works in all the latest browsers, including Chrome, Firefox, Safari, and even Edge.

What is local storage?

Local storage is a feature of the Web Storage API that allows web developers to store key-value pairs in a user’s web browser. The stored data is persistent, which means it will remain available even after the user closes and reopens the browser, or even after the computer is turned off and on again.

Local storage is useful for storing small amounts of data that are required by a web application, such as user preferences, session data, and application settings. Local storage can be accessed and modified using JavaScript methods provided by the Web Storage API.

Here’s an example of how to set and get a value in local storage using JavaScript:

To set a value in local storage:

localStorage.setItem('key', 'value');

To get a value from local storage:

var value = localStorage.getItem('key');

Note that local storage is subject to a storage limit, which is typically around 5-10 megabytes, depending on the browser. Also, the data stored in local storage is not encrypted, so it should not be used to store sensitive information such as passwords or credit card numbers.

A practical example of how to use local storage to store and retrieve user preferences for a website:

<!-- HTML code for the website -->
<label for="theme">Select a theme:</label>
<select id="theme" onchange="savePreference()">
  <option value="light">Light</option>
  <option value="dark">Dark</option>
</select>

<script>
  // JavaScript code to save and retrieve user preferences using local storage
  var themeSelect = document.getElementById("theme");
  
  // Set the initial value of the theme select box from local storage, if available
  if (localStorage.getItem("theme")) {
    themeSelect.value = localStorage.getItem("theme");
  }
  
  // Function to save the user's theme preference to local storage
  function savePreference() {
    localStorage.setItem("theme", themeSelect.value);
  }
</script>

In this example, we have a select box for the user to choose between a light and dark theme. When the user selects a theme, the savePreference function is called, which saves the selected theme to local storage using the localStorage.setItem method.

On subsequent visits to the website, the initial value of the theme select box is set from local storage using the localStorage.getItem method.

This is just one example of how local storage can be used in a practical way to enhance the user experience of a website.

Q/A

1. What is local storage and how is it different from session storage?

• Local storage is a web API that allows you to store key-value pairs in a user’s web browser for long-term storage. It is different from session storage in that data stored in local storage persists even after the browser is closed, while session storage data is cleared when the browser is closed or the session ends.

2. What is the maximum amount of data that can be stored in local storage?

• The maximum amount of data that can be stored in local storage varies by browser, but is generally around 5-10 MB.

3. How do you store and retrieve data from local storage in JavaScript?

• To store data in local storage, you can use the localStorage.setItem() method, passing in a key-value pair as arguments. To retrieve data from local storage, you can use the localStorage.getItem() method, passing in the key of the value you want to retrieve.

4. Can local storage data be accessed by other websites or domains?

• Local storage data can only be accessed by the website that stored it. Other websites or domains cannot access or modify local storage data.

5. Is local storage data encrypted or secured in any way?

• Local storage data is not encrypted by default, so sensitive information should not be stored in local storage. However, you can encrypt data before storing it in local storage using JavaScript encryption libraries or other techniques.

6. How can you clear or delete data from local storage?

• To clear or delete data from local storage, you can use the localStorage.removeItem() method, passing in the key of the value you want to remove. To clear all data from local storage, you can use the localStorage.clear() method.

7. What happens to local storage data when the browser is closed or the device is turned off?

• Local storage data persists even after the browser is closed or the device is turned off, and can be retrieved the next time the website is visited.

8. How do you check if local storage is available and supported in the user’s browser?

• You can check if local storage is available and supported in the user’s browser by checking the value of the window.localStorage property. If the value is null or undefined, local storage is not supported in the browser.

9. What are some common use cases for local storage?

• Local storage can be used for storing user preferences, login credentials, shopping cart items, and other application-specific data that needs to persist across browser sessions.

10. Are there any security concerns or risks associated with using local storage?

• Yes, there are security concerns associated with using local storage, particularly with storing sensitive information. Local storage data is not encrypted by default, and can be accessed by other JavaScript code on the same website. Additionally, malicious third-party scripts can potentially access local storage data through cross-site scripting (XSS) attacks.

What is session storage?

Session storage is a feature of the Web Storage API that allows web developers to store key-value pairs in a user’s web browser for the duration of a session. A session is defined as the period of time that a user spends on a website, from the moment they open the site until the moment they close their browser or navigate away from the site.

Session storage is similar to local storage, but with a key difference: the data stored in session storage is only available for the duration of the session, and is cleared when the user closes their browser or navigates away from the site.

Like local storage, session storage is useful for storing small amounts of data that are required by a web application, such as user preferences, session data, and application settings. Session storage can be accessed and modified using JavaScript methods provided by the Web Storage API.

Here’s an example of how to set and get a value in session storage using JavaScript:

To set a value in session storage:

sessionStorage.setItem('key', 'value');

To get a value from session storage:

var value = sessionStorage.getItem('key');

Note that like local storage, the data stored in session storage is not encrypted, so it should not be used to store sensitive information such as passwords or credit card numbers.

Here is a practical example of how to use session storage to store and retrieve session data for a website:

<!-- HTML code for the website -->
<label for="name">Enter your name:</label>
<input type="text" id="name" onblur="saveSessionData()">

<script>
  // JavaScript code to save and retrieve session data using session storage
  var nameInput = document.getElementById("name");
  
  // Set the initial value of the name input from session storage, if available
  if (sessionStorage.getItem("name")) {
    nameInput.value = sessionStorage.getItem("name");
  }
  
  // Function to save the user's name input to session storage
  function saveSessionData() {
    sessionStorage.setItem("name", nameInput.value);
  }
</script>

In this example, we have an input field for the user to enter their name. When the user enters their name and then clicks outside of the input field (using the onblur event), the saveSessionData function is called, which saves the entered name to session storage using the sessionStorage.setItem method.

On subsequent visits to the website within the same session, the initial value of the name input is set from session storage using the sessionStorage.getItem method.

This is just one example of how session storage can be used in a practical way to store and retrieve session data for a website. Note that the data stored in session storage is cleared when the user closes their browser or navigates away from the site, so it should not be used to store data that needs to persist across sessions.

Here’s an example of how to use session storage to store and retrieve session data across three pages:

Page 1:

<!-- HTML code for page 1 -->
<label for="name">Enter your name:</label>
<input type="text" id="name" onblur="saveSessionData()">
<a href="page2.html">Go to Page 2</a>

<script>
  // JavaScript code to save session data using session storage
  var nameInput = document.getElementById("name");
  
  // Function to save the user's name input to session storage
  function saveSessionData() {
    sessionStorage.setItem("name", nameInput.value);
  }
</script>

Page 2:

<!-- HTML code for page 2 -->
<p>Welcome to page 2!</p>
<a href="page3.html">Go to Page 3</a>

<script>
  // JavaScript code to retrieve session data from session storage
  var nameDisplay = document.getElementById("name-display");
  
  // Set the inner HTML of the name display from session storage, if available
  if (sessionStorage.getItem("name")) {
    nameDisplay.innerHTML = "Hello, " + sessionStorage.getItem("name") + "!";
  }
</script>

Page 3:

<!-- HTML code for page 3 -->
<p>Welcome to page 3!</p>
<a href="page1.html">Go back to Page 1</a>

<script>
  // JavaScript code to retrieve session data from session storage
  var nameDisplay = document.getElementById("name-display");
  
  // Set the inner HTML of the name display from session storage, if available
  if (sessionStorage.getItem("name")) {
    nameDisplay.innerHTML = "Hello, " + sessionStorage.getItem("name") + "!";
  }
</script>

In this example, we have three pages with a simple input field on the first page where the user can enter their name. When the user clicks outside of the input field, the saveSessionData function is called, which saves the entered name to session storage using the sessionStorage.setItem method.

On the second and third pages, the user is welcomed by name using the sessionStorage.getItem method to retrieve the name from session storage and display it in a message.

Note that since we are using session storage, the data stored in it will persist across multiple pages within the same browsing session, but will be cleared when the user closes their browser or navigates away from the site.

Q/A

1. What is session storage and how is it different from local storage?

• Session storage is a web API that allows you to store key-value pairs in a user’s web browser for the duration of a session, which typically ends when the browser is closed. It is different from local storage in that data stored in session storage is cleared when the browser is closed or the session ends, while local storage data persists across browser sessions.

2. How do you store and retrieve data from session storage in JavaScript?

• To store data in session storage, you can use the sessionStorage.setItem() method, passing in a key-value pair as arguments. To retrieve data from session storage, you can use the sessionStorage.getItem() method, passing in the key of the value you want to retrieve.

3. Can session storage data be accessed by other websites or domains?

• Session storage data can only be accessed by the website that stored it. Other websites or domains cannot access or modify session storage data.

4. Is session storage data encrypted or secured in any way?

• Session storage data is not encrypted by default, so sensitive information should not be stored in session storage. However, you can encrypt data before storing it in session storage using JavaScript encryption libraries or other techniques.

5. How can you clear or delete data from session storage?

• To clear or delete data from session storage, you can use the sessionStorage.removeItem() method, passing in the key of the value you want to remove. To clear all data from session storage, you can use the sessionStorage.clear() method.

6. What happens to session storage data when the browser is closed or the session ends?

• Session storage data is cleared when the browser is closed or the session ends, which can occur when the user logs out, closes the browser, or after a certain period of inactivity.

7. How do you check if session storage is available and supported in the user’s browser?

• You can check if session storage is available and supported in the user’s browser by checking the value of the window.sessionStorage property. If the value is null or undefined, session storage is not supported in the browser.

8. What are some common use cases for session storage?

• Session storage can be used for storing user authentication tokens, temporary form data, and other application-specific data that needs to persist across multiple pages within a single browser session.

9. Are there any limitations or drawbacks to using session storage?

• The main limitation of session storage is that data is cleared when the browser is closed or the session ends, so it cannot be used for long-term storage. Additionally, session storage data is only accessible within a single browser session, so it cannot be shared across multiple devices or browsers.

10. Are there any security concerns or risks associated with using session storage?

• Yes, there are security concerns associated with using session storage, particularly with storing sensitive information. Session storage data is not encrypted by default, and can be accessed by other JavaScript code on the same website. Additionally, malicious third-party scripts can potentially access session storage data through cross-site scripting (XSS) attacks.

What is cookie?

A cookie is a small piece of data that is sent from a website to a user’s web browser and stored on their device. Cookies are commonly used to store information about the user’s activity on the website, such as their login credentials or preferences, and are sent back to the website on subsequent visits.

Here’s a practical example of how to use cookies in JavaScript to store and retrieve a user’s name:

<!-- HTML code for the website -->
<label for="name">Enter your name:</label>
<input type="text" id="name">
<button onclick="saveCookie()">Save Name</button>
<button onclick="getCookie()">Get Name</button>

<script>
  // JavaScript code to save and retrieve a user's name using cookies
  var nameInput = document.getElementById("name");
  
  // Function to save the user's name to a cookie
  function saveCookie() {
    document.cookie = "name=" + nameInput.value + "; expires=" + new Date(new Date().getTime() + 86400000).toUTCString() + "; path=/";
  }
  
  // Function to retrieve the user's name from a cookie
  function getCookie() {
    var name = document.cookie.replace(/(?:(?:^|.*;\s*)name\s*\=\s*([^;]*).*$)|^.*$/, "$1");
    alert("Hello, " + name + "!");
  }
</script>

In this example, we have an input field for the user to enter their name, and two buttons for saving and retrieving the name using cookies. When the user enters their name and clicks the “Save Name” button, the saveCookie function is called, which creates a cookie with the name and value of the entered name, and an expiration date set to one day from the current time. The cookie is stored in the browser’s cookie jar and can be accessed by other pages on the same domain.

When the user clicks the “Get Name” button, the getCookie function is called, which retrieves the name from the cookie using a regular expression to extract the value of the “name” cookie. The name is then displayed in an alert box.

Note that cookies have limitations, such as a maximum size and the fact that they can be disabled by the user’s browser settings. Also, sensitive information should not be stored in cookies as they are stored in plain text and can be accessed by malicious third parties.

Q/A

1. What is a cookie and how is it used in web development?

• A cookie is a small text file that is stored on a user’s device by a web server. Cookies are used to store information about the user’s preferences, login status, and other session data, which can be used to personalize the user’s experience on a website.

2. How are cookies different from session storage and local storage?

• Cookies are different from session storage and local storage in that they are stored on the server, not the client. Cookies are also limited in size, with a maximum size of around 4KB, while session storage and local storage can store much larger amounts of data.

3. How can you create a cookie in JavaScript?

• To create a cookie in JavaScript, you can use the document.cookie property to set the value of the cookie. For example, document.cookie = "username=John Doe";.

4. How can you read the value of a cookie in JavaScript?

• To read the value of a cookie in JavaScript, you can access the document.cookie property, which returns a string containing all the cookies stored on the user’s device. You can then parse the string to extract the value of the cookie you want to read.

5. Can cookies be accessed by other websites or domains?

• Cookies can only be accessed by the website that created them. However, third-party cookies can be used to track user behavior across multiple websites or domains.

6. What are the different types of cookies?

• There are two main types of cookies: session cookies and persistent cookies. Session cookies are deleted when the user closes the browser, while persistent cookies remain on the user’s device for a specified period of time.

7. How can you set the expiration time of a cookie?

• You can set the expiration time of a cookie by including the expires attribute in the cookie string. For example, document.cookie = "username=John Doe; expires=Wed, 01 Jan 2025 00:00:00 UTC";.

8. How can you delete a cookie in JavaScript?

• To delete a cookie in JavaScript, you can set the value of the cookie to an empty string and set the expiration time to a past date. For example, document.cookie = "username=; expires=Thu, 01 Jan 1970 00:00:00 UTC";.

9. Are there any security concerns or risks associated with using cookies?

• Yes, there are security concerns associated with using cookies, particularly with storing sensitive information. Cookies can be intercepted or modified by malicious third parties, and can be used for tracking user behavior across multiple websites or domains.

10. How can you secure cookies using HTTP-only and secure flags?

• You can secure cookies by setting the HTTP-only flag, which prevents JavaScript code from accessing the cookie, and the secure flag, which ensures that the cookie is only sent over an HTTPS connection. For example, document.cookie = "username=John Doe; HttpOnly; secure";.