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Browser Window Interaction in JavaScript

JavaScript Fundamentals: Interaction: alert, prompt, confirm

In the JavaScript community, what is the commonly used name for the alert window?​

View Answer:
Interview Response: The JavaScript alert window is commonly referred to as an "alert box", "pop-up" or “modal.”

How does the alert function work?​

View Answer:
Interview Response: The alert() function in JavaScript displays a pop-up window with a message to the user. The function takes a string argument which is the message to be displayed. The alert blocks further execution of the code until the user dismisses the alert by clicking "OK".

Code Example:

alert('Hello, JavaScript!');

What data type does the alert window method return?​

View Answer:
Interview Response: The alert() window method in JavaScript does not return a specific data type or value.

How does the prompt function work in simple terms?​

View Answer:
Interview Response: It shows a window with text and a request for input, then returns a string.

Technical Response: The window prompt() in JavaScript displays a pop-up window with a message and an input field, allowing the user to input a value. The function returns the value entered by the user as a string, or null if the user cancels the prompt. The window prompt() takes two optional arguments: a message string to display and a default value for the input field.

Code Example:

let userName = prompt("Please enter your name:", "Harry Potter");

if (userName) {
    console.log(`Hello, ${userName}!`);
} else {
    console.log("No name entered.");
}

In this example, the prompt() function displays a dialog box asking the user to enter their name. The text "Please enter your name:" is the prompt, and "Harry Potter" is the default input text. The function returns the input from the user as a string. If the user clicks "OK" without entering a name, or if the user clicks "Cancel", the function returns null.

Please note that prompt() is a method of the window object and only works in the browser environment, it won't work in server-side JavaScript environments like Node.js.

Also, the usage of prompt is not recommended for modern web development practices due to usability and user experience concerns. It blocks the browser interaction until the user responds which creates a bad user experience, and moreover, some browsers may also ignore these dialogs. Consider using more user-friendly interfaces like form controls or modal windows for user input.

How many arguments does the window prompt accept?​

View Answer:
Interview Response: The window prompt accepts two arguments: a message to display and a default value for the input field.

Code Example:

// the brackets denote that the parameter is not required 

result = prompt(title, [default]);

What does the prompt return when the prompt its escaped or canceled?​

View Answer:
Interview Response: When the prompt is canceled or escaped, the window prompt returns null.

Why is it essential to provide a second argument (default) for the prompt function?​

View Answer:
Interview Response: Providing a second argument, or default, for the prompt function in JavaScript is essential because it provides an initial value for the input field. This approach ensures that the browser (internet explorer) does not return undefined.

Technical Response: There is a chance that the user is using a browser such as Internet Explorer, which returns undefined if there is no default. This action could have ramifications that could affect the application adversely.

How does the confirm function work?​

View Answer:
Interview Response: Confirm produces a window with a Boolean question of OK and Cancel. Ok returns true, and Cancel returns false.

Technical Response: The confirm function shows a modal window with a question and two buttons: OK and Cancel. The result is true if OK is pressed and false otherwise.

Code Example:

let isBoss = confirm('Are you the boss?');

console.log(isBoss); // true if OK is pressed and false otherwise

The alert, prompt, and confirm methods are part of what object model?​

View Answer:
Interview Response: The alert(), prompt(), and confirm() methods are part of the Window object in the Browser Object Model (BOM).

Technical Response: The alert, prompt, and confirm methods belong to the Browser Object Model. It is commonly called the BOM.

What is the difference between the window and browser object models?​

View Answer:
Interview Response: The Window Object Model (WOM) focuses on the browser's window, while the Browser Object Model (BOM) encompasses the entire browser environment, including the Window object.

What are two limitations shared by the alert, prompt, and confirm methods?​

View Answer:
Interview Response: Two limitations shared by the alert, prompt, and confirm methods in JavaScript are that they are blocking, which means they pause the execution of code until the user responds, and they have limited to no styling options. We have no control over the position and look of the modal window.

Technical Response:

  1. The browser determines the exact location of the modal window. Usually, it is in the center.
  2. The exact look of the window also depends on the browser, and we cannot modify it.

Can you explain the difference between window.onload and the DOMContentLoaded event?​

View Answer:
Interview Response: window.onload activates after the whole page, including external resources, finishes loading. DOMContentLoaded occurs when the DOM is ready, but may not wait for images and other external resources to finish loading.

How do you open a new browser window using JavaScript?​

View Answer:
Interview Response: You can use the window.open() method in JavaScript, providing the URL and target ('_blank' for a new window) as arguments to open a new browser window.

Code Example:

// Opens a new window and navigates it to a specific URL
let newWindow = window.open('https://www.example.com', '_blank');

// Checks if the new window was blocked
if(newWindow === null || typeof(newWindow)=='undefined'){ 
   alert('Please disable your pop-up blocker and click the "Open" link again.'); 
} else { 
   newWindow.focus();
}

In this code:

  • window.open('https://www.example.com', '_blank') opens a new window or tab (depending on the user's browser settings) and loads 'https://www.example.com' in it. '_blank' is used to specify that a new window or tab should be opened.
  • The if condition checks whether the pop-up window was blocked. If the pop-up was blocked, window.open() will return null or undefined.
  • newWindow.focus() brings the new window or tab to the front.

Please note, as this function can be misused to open unwanted pop-ups, some browsers and pop-up blockers may restrict its usage. Ensure to use this method in a way that enhances user experience and respects user preferences.

How do you resize a browser window using JavaScript?​

View Answer:
Interview Response: You can use the window.resizeTo() method to resize a browser window. It takes two arguments, the width, and height of the window in pixels.

Here's a simple example:

// Resizing the window to a width of 500px and a height of 400px
window.resizeTo(500, 400);

In this example, window.resizeTo(500, 400); resizes the current window to 500 pixels wide and 400 pixels tall.

Please note, the resizeTo() method might not work as expected in all modern browsers due to user preferences and browser settings. Some browsers might not support this method, or they might only support it if the window was originally opened with JavaScript using window.open(). The usage of such methods that manipulate the user's browser window are generally considered a bad practice as it takes control away from the user.

How do you close a browser window using JavaScript?​

View Answer:
Interview Response: You can use the window.close() method to close the current browser window.

Code Example:

<!DOCTYPE html>
<html>
<head>
<title>Close Window</title>
</head>
<body>
<h1>Close Window</h1>
<button onclick="closeWindow()">Close Window</button>
<script>
function closeWindow() {
  window.close();
}
</script>
</body>
</html>

How do you check if a pop-up window is blocked by the browser?​

View Answer:
Interview Response: In JavaScript, you can check if a pop-up window is blocked by the browser by testing if window.open() returns null or undefined. If it does, the pop-up was blocked.

Code Example:

let newWindow = window.open('https://www.example.com', '_blank');

if (newWindow === null || typeof(newWindow) == 'undefined') {
    console.log('The pop-up was blocked.');
} else {
    console.log('The pop-up was not blocked.');
    newWindow.focus();
}

How do you detect the current browser window size using JavaScript?​

View Answer:
Interview Response: You can use the window.innerWidth and window.innerHeight properties to get the current size of the browser window.

Code Example:

let windowWidth = window.innerWidth;
let windowHeight = window.innerHeight;

console.log(`Current window width is ${windowWidth} pixels and height is ${windowHeight} pixels.`);

Please note that innerWidth and innerHeight include the width and height of the scrollbar if it's visible. If you need the width and height without the scrollbar, you can use document.documentElement.clientWidth and document.documentElement.clientHeight respectively.

How do you scroll to a specific location on a page using JavaScript?​

View Answer:
Interview Response: You can use the window.scrollTo() method to scroll to a specific location on a page. It takes two arguments, the x and y coordinates of the location to scroll to.

How do you detect if a browser supports cookies using JavaScript?​

View Answer:
Interview Response: You can use the navigator.cookieEnabled property to detect if a browser supports cookies. It returns a boolean value indicating whether cookies are enabled. To manually detect if a browser supports cookies using JavaScript, you can create a test cookie, and then check if it exists and delete it afterward.

How do you prevent a browser from caching a page using JavaScript?​

View Answer:
Interview Response: You can use the Cache-Control and Pragma headers in the HTTP response to prevent a browser from caching a page. Alternatively, you can append a random query string to the URL of the page.

How do you detect the current URL of a browser window using JavaScript?​

View Answer:
Interview Response: You can use the window.location.href property to get the current URL of a browser window.