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Ques: What is the Browser Object Model (BOM)?
Ans: The BOM (Browser Object Model) allows JavaScript to interact with the browser environment — not just the webpage (DOM).
It gives access to browser-specific objects like window, navigator, screen, location, history, and more.
Example:
console.log(window.innerWidth); // Get browser width
Ques: What is the window object in JavaScript?
Ans: The window object is the top-level global object in browsers.
All global JavaScript variables, functions, and objects automatically become properties of window.
Example:
window.alert("Hello!");
console.log(window.innerHeight);
Ques: What are some commonly used window properties?
window.innerHeight, window.innerWidth → browser’s viewport sizewindow.location → URL infowindow.navigator → browser infowindow.screen → device screen detailswindow.history → navigation historywindow.document → access DOMQues: What are some important window methods?
window.alert() – Displays an alert boxwindow.confirm() – Asks for confirmationwindow.prompt() – Takes user inputwindow.open() – Opens a new window or tabwindow.close() – Closes the current windowExample:
if (confirm("Are you sure?")) {
alert("Confirmed!");
}
Ques: What is the screen object in JavaScript?
Ans: The screen object provides information about the user’s display monitor.
Example:
console.log(screen.width);
console.log(screen.height);
Common properties:
screen.width, screen.height → screen resolutionscreen.availWidth, screen.availHeight → available space excluding OS barsscreen.colorDepth → bit depth for color displayQues: What is the location object used for?
Ans: The location object represents the current URL and allows redirection or reloading of pages.
Example:
console.log(location.href); // Full URL
location.href = "<https://google.com>"; // Redirects
Common properties & methods:
location.href → full URLlocation.hostname → domain namelocation.pathname → file pathlocation.protocol → http / httpslocation.reload() → reloads pageQues: How can you reload or redirect a webpage using JavaScript?
location.reload(); // Reloads current page
location.href = "<https://example.com>"; // Redirects to another page
Ques: What is the history object in JavaScript?
Ans: The history object allows navigation through the browser’s session history.
Example:
history.back(); // Go to previous page
history.forward(); // Go to next page
Methods:
history.back() – Same as browser back buttonhistory.forward() – Same as next buttonhistory.go(n) – Moves n steps in history (negative for back)Ques: What is the navigator object?
Ans: The navigator object gives information about the browser and system environment.
Example:
console.log(navigator.userAgent);
console.log(navigator.language);
Common properties:
navigator.userAgent → browser detailsnavigator.language → user’s preferred languagenavigator.onLine → check if onlinenavigator.platform → OS infonavigator.geolocation → access location (with permission)Ques: How do you detect the browser type in JavaScript?
console.log(navigator.userAgent);
Example Output:
Mozilla/5.0 (Windows NT 10.0; Win64; x64)
Ques: How can you display popups in JavaScript?
Alert box
alert("Welcome!");
Confirm box
if (confirm("Are you sure?")) console.log("Yes");
Prompt box
let name = prompt("Enter your name:");
alert("Hello " + name);
Ques: What is the difference between alert(), confirm(), and prompt()?
| Method | Description | Returns |
|---|---|---|
alert() | Displays a message | undefined |
confirm() | Asks user to confirm | true / false |
prompt() | Takes user input | text / null |
Ques: What are JavaScript timing events?
Ans: Timing events execute code after a delay or repeatedly.
setTimeout() → executes once after delaysetInterval() → repeats at intervalsclearTimeout() / clearInterval() → stop timersExample:
setTimeout(() => console.log("Hello after 2s"), 2000);
Ques: What is the difference between setTimeout() and setInterval()?
| Method | Description |
|---|---|
setTimeout(fn, delay) | Runs code once after delay |
setInterval(fn, delay) | Runs code repeatedly every interval |
Example:
setInterval(() => console.log("Repeating..."), 1000);
Ques: How can you stop a timer in JavaScript?
let id = setInterval(() => console.log("Running"), 1000);
clearInterval(id); // stops repeating
Ques: What are cookies in JavaScript?
Ans: Cookies are small pieces of data stored on the user’s browser to remember information (like login or preferences).
Example:
document.cookie = "username=John; expires=Fri, 31 Dec 2025 12:00:00 UTC; path=/";
Ques: How can you read cookies using JavaScript?
console.log(document.cookie);
Ques: How can you delete a cookie?
Ans: Set the cookie’s expiry date to the past:
document.cookie = "username=; expires=Thu, 01 Jan 1970 00:00:00 UTC;";
Ques: What are the limitations of cookies?
Ques: What are alternatives to cookies in modern web apps?
Ques: What is the difference between BOM and DOM?
| Feature | DOM | BOM |
|---|---|---|
| Full Form | Document Object Model | Browser Object Model |
| Purpose | Interacts with page content | Interacts with browser environment |
| Main Object | document | window |
| Example | document.getElementById() | window.alert() |
Ques; How can you detect if the user is online or offline?
if (navigator.onLine) {
console.log("Online");
} else {
console.log("Offline");
}
Ques: How can you get the user’s location using BOM?
navigator.geolocation.getCurrentPosition(
(pos) => console.log(pos.coords.latitude, pos.coords.longitude),
(err) => console.error(err)
);
Ques: What is the window.open() method used for?
Ans: Opens a new browser tab or window:
window.open("<https://example.com>", "_blank");
Ques: What are common use cases of the BOM?