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Popups / Window Methods

Frames / Windows: Popups and Window Methods

What is a JavaScript popup window?​

View Answer:
Interview Response: A popup window is a new browser window opened by JavaScript, typically to display additional information without leaving the current page.

What is the JavaScript method to open a popup window?​

View Answer:
Interview Response: The JavaScript method to open a popup window is `window.open()`. It accepts parameters for URL, window name, and window features like dimensions and toolbar visibility.

Code Example:

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

if (newWindow) {
    newWindow.focus();
} else {
    alert('Please allow popups for this website');
}

Can users prevent or block a JavaScript popup window?​

View Answer:
Interview Response: Yes, users can block JavaScript popup windows using their web browser's built-in pop-up blocker settings, browser extensions, or adjusting privacy settings to disallow JavaScript execution.

What are some of the parameters that you can use in 'window.open()'?​

View Answer:
Interview Response: `window.open()` parameters include: URL (page to load), window name, and a features string defining window size (height, width), position (left, top), and visibility of elements (toolbar, scrollbars).

Code Example:

let newWindow = window.open(
  'https://www.example.com', 
  '_blank', 
  'toolbar=yes,scrollbars=yes,resizable=yes,top=500,left=500,width=400,height=400'
);

if (newWindow) {
    newWindow.focus();
} else {
    alert('Please allow popups for this website');
}

Can you communicate between a popup and its parent window?​

View Answer:
Interview Response: Yes, a popup and its parent window can communicate via JavaScript if they're from the same origin, using methods like `window.opener` and `window.postMessage()`.

Code Example:

Here's a simple example of communication between a parent window and a popup window.

In your main HTML file:

// Open a new window
var popup = window.open('popup.html', 'popupWindow');

// Send a message to the popup after it loads
popup.onload = function() {
    popup.postMessage("Hello Popup!", "*");
}

And then in your popup.html file:

// Listen for messages from the parent window
window.addEventListener('message', function(event) {
    console.log('Received message:', event.data);
}, false);

This code opens a new window with the URL 'popup.html', and once it's loaded, sends a message to it. The popup window listens for incoming messages and logs them to the console. Please note that for security reasons, using "*" as target origin in postMessage is not recommended for production code.

What happens when a popup is blocked by a browser?​

View Answer:
Interview Response: When a popup is blocked by a browser, the `window.open()` method returns `null` and the browser may notify the user about the blocked popup, depending on its settings.

Can a popup window navigate its opener window?​

View Answer:
Interview Response: Yes, a popup window can navigate its opener window by using the `window.opener.location` property, assuming they are from the same origin due to the same-origin policy.

Code Example:

// Open a new window
let newWindow = window.open('', '_blank');

if (newWindow) {
    // Use the opener property to navigate the original window
    newWindow.opener.location.href = 'https://www.example.com';
} else {
    alert('Please allow popups for this website');
}

Can you explain the function of the 'window.open()' method?​

View Answer:
Interview Response: The `window.open()` method opens a new browser window or a new tab, with an optional specified URL and name, and returns a reference to the new window.

Technical Response: A pop-up window is one of the oldest methods to show an additional document to a user. The Window interface's open() method loads the specified resource into the new or existing browsing context (window, ‹iframe› or tab) with the specified name. If the name does not exist, a new browsing context opens in a new tab or a new window, and the specified resource is loaded. The open method takes three parameters: URL, windowName, and windowFeatures. The URL is a DOMString that specifies the location of the resource to be loaded. This element can be a path or URL to an HTML page, an image file, or any other resource that the browser supports. The windowName is a DOMString specifying the browsing context's name (window, ‹iframe› or tab) to load the specified resource; if the name does not indicate an existing context, a new window is created and gives the name specified by windowName. The windowFeatures parameter is a DOMString that contains a comma-separated list of window characteristics and their values in the form "name=value". These features include settings such as the window's default size and location, as well as whether or not the toolbar is shown. The string must not include any spaces. Both the windowName and windowFeatures options are optional.

Code Example: Basic Implementation

Syntax: var window = window.open(url, windowName, [windowFeatures]);

var windowObjectReference;
var windowFeatures =
  'menubar=yes,location=yes,resizable=yes,scrollbars=yes,status=yes';

function openRequestedPopup() {
  windowObjectReference = window.open(
    'http://www.cnn.com/',
    'CNN_WindowName',
    windowFeatures
  );
}

When do browsers block pop-up events?​

View Answer:
Interview Response: Most browsers block pop-ups if they are called outside of user-triggered event handlers like onclick. This way, users are somewhat protected from unwanted pop-ups, but the functionality is not disabled totally.

Code Example:

// popup blocked
window.open('https://javascript.info');

// popup allowed
button.onclick = () => {
  window.open('https://javascript.info');
};

What happens when a pop-up opens from onclick, but after setTimeout?​

View Answer:
Interview Response: The pop-up may still be blocked as some browsers consider `setTimeout` as breaking the direct sequence of user-triggered events, thus viewing it as potentially unwanted.

Technical Response: The simple answer is that it depends on the browser. For instance, if an onclick event has a nested timeout and returns a window open after 3 seconds. The popup opens in Chrome but gets blocked in Firefox. If we decrease the delay, the pop-up works in Firefox (down to 2 seconds or less). The difference is that Firefox accepts timeouts of 2000ms or less, but beyond that, It eliminates the "trust," presuming that it is now "outside of the user action." As a result, the first one gets denied while the second is not.

Code Example:

// open after 3 seconds - works in Chrome, but not Firefox
setTimeout(() => window.open('http://google.com'), 3000);

// open after 1 seconds works in Firefox too...
setTimeout(() => window.open('http://google.com'), 1000);

What is essential to remember when configuring 'window.open()' parameters?​

View Answer:
Interview Response: The configuration string for the new window. It contains settings delimited by a comma. There must be no spaces in parameters, for example: 'width=200,height=100'.

Code Example:

let params = `scrollbars=no,resizable=no,status=no,location=no,toolbar=no`;

open('/', 'test', params);

What are the rules for omitted settings in the 'window.open()' method?​

View Answer:
Technical Response: In `window.open()`, if settings are omitted, a new window opens with the following default values: fully visible toolbar, location bar, status bar, and menus. Pop-up blocker rules may affect behavior.

Technical Response: There are several rules for omitted settings of the Window.open() method.

  • If there is no third argument or nothing in the open call, the default window parameters return.
  • If a string of params is present but specific yes/no features are missing, the missed features are believed to be null. So, if you supply params, make sure that all needed features explicitly set to yes.
  • If no left/top parameters are specified, the browser attempts to start a new window near the previous one that launched.
  • If no width/height is specified, the new window turns out to be the same size as the previous one.

Code Example:

let params = `scrollbars=no,resizable=no,status=no,location=no,toolbar=no`;

open('/', 'test', params);

What is the origin policy when it comes to pop-up windows?​

View Answer:
Interview Response: Pop-up windows follow the same-origin policy: a script can only access properties/methods of a window from the same origin (protocol, domain, and port) to prevent cross-site scripting (XSS) attacks.

Can a pop-up access the “opener” window and make modifications?​

View Answer:
Interview Response: A pop-up may access the (opener) window using window.opener reference and it is null for all windows except pop-ups. As a result, the relationship between the windows is bidirectional: the main window and the pop-up both refer to one other.

Code Example:

// Open a new window
let newWindow = window.open('', '_blank');

if (newWindow) {
    // Use the opener property to access and modify the original window
    newWindow.opener.document.body.innerHTML = "<h1>This is changed by the popup</h1>";
} else {
    alert('Please allow popups for this website');
}

Is there a way we can close a pop-up window programmatically?​

View Answer:
Interview Response: Yes, we can close a pop-up window programmatically using the `window.close()` method from the pop-up window's context.

Technical Response: Yes, the close() method is available for any window, but most browsers ignore window.close() if the window does not get created with window.open(). So, it only works on a pop-up. If the window is closed, the closed attribute is true. This behavior is important for determining whether or not the pop-up (or the main window) is still active. A user can close it at any time, and our programming should take that into account. To check if a window is closed: win.closed.

Code Example:

let newWindow = open('/', 'example', 'width=300,height=300');

newWindow.onload = function () {
  newWindow.close(); // method
  alert(newWindow.closed); // property
};

Can a user distinguish between a user-initiated popup and a script-initiated one?​

View Answer:
Interview Response: No, from a user's perspective, it's generally not possible to distinguish between a user-initiated and a script-initiated popup, as both appear as new browser windows or tabs.

Is it possible to open popups in full screen?​

View Answer:
Interview Response: Yes, JavaScript `window.open()` can request full-screen mode using features like `fullscreen=yes`, but most modern browsers restrict or ignore this due to user experience concerns and potential security issues.

Can you customize the appearance of a JavaScript popup window?​

View Answer:
Interview Response: Yes, to an extent, by defining window features in the `window.open()` method parameters.

What are some alternatives to JavaScript popups for displaying information?​

View Answer:
Interview Response: Modal dialogs, tooltips, or information displayed directly in the page can be used instead of popups.

Can you move or resize a JavaScript popup window after it has opened?​

View Answer:
Interview Response: Yes, the `moveTo()`, `moveBy()`, `resizeTo()`, and `resizeBy()` methods allow to move or resize the popup.

Code Example:

function openWindow() {
  let newWindow = window.open('https://www.hellojavascript.info', '_blank', 'width=200,height=200');

  if (newWindow) {
    newWindow.moveTo(40, 40);
    newWindow.resizeTo(400, 400);
  } else {
    alert('Please allow popups for this website');
  }
}

const button = document.querySelector('button');

button.addEventListener('click', function() {
openWindow();
})

How do you close a popup window using JavaScript?​

View Answer:
Interview Response: The `window.close()` method is used to close a popup window.

Code Example:

// Open a new window
let newWindow = window.open('', '_blank');

if (newWindow) {
    // Do something with the new window

    // Close the new window
    newWindow.close();
} else {
    alert('Please allow popups for this website');
}

Can JavaScript detect if a popup has been closed?​

View Answer:
Interview Response: Yes, by checking the `window.closed` property of the popup window object.

Code Example:

let newWindow = window.open('', '_blank');

if (newWindow) {
    // Do something with the new window

    // Check if the new window has been closed
    if (newWindow.closed) {
        console.log('The popup has been closed');
    } else {
        console.log('The popup is still open');
    }
} else {
    alert('Please allow popups for this website');
}

How can you give focus to a popup window?​

View Answer:
Interview Response: You can give focus to a popup window using the focus() method in JavaScript.

Code Example:

let newWindow = window.open('', '_blank');

if (newWindow) {
    // Do something with the new window

    // Give focus to the new window
    newWindow.focus();
} else {
    alert('Please allow popups for this website');
}

Can you prevent a popup from gaining focus?​

View Answer:
Interview Response: Yes, using `window.blur()` on the popup window prevents it from gaining focus.

Code Example:

<!DOCTYPE html>
<html>
<body>

<h1>The Window Object</h1>
<h2>The window.blur() Method</h2>

<p>Click the button to open a new window, and blur it (remove focus from it).</p>

<button onclick="windowFunction()">Try it</button>

<script>
function windowFunction() {
  let newWindow = window.open("", "", "width=200, height=100");
  newWindow.blur();
}
</script>

</body>
</html>

Can a JavaScript popup window be modal?​

View Answer:
Interview Response: No, JavaScript popup windows cannot be made truly modal (blocking user interaction with other windows) using native JavaScript methods. However, you can create a modal-like experience by overlaying a semi-transparent div or dialog over the parent window.

Code Example:

<!DOCTYPE html>
<html>
<head>
  <style>
    /* CSS for modal overlay */
    #modal-overlay {
      position: fixed;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
      background-color: rgba(0, 0, 0, 0.5);
      z-index: 9999;
    }
  </style>
</head>
<body>
  <button onclick="openModal()">Open Modal</button>

  <div id="modal-overlay" style="display: none;"></div>

  <script>
    function openModal() {
      // Show modal overlay
      document.getElementById('modal-overlay').style.display = 'block';

      // Other modal operations
      // ...
    }
  </script>
</body>
</html>

Can you restrict actions in the main window when a popup is open?​

View Answer:
Interview Response: JavaScript doesn't support this natively. However, you can create a modal-like effect using CSS and JavaScript together.