JavaScript Basics

JavaScript has three built-in popup boxes: Alert (displays a message), Confirm (asks for OK/Cancel confirmation), and Prompt (requests user input). Radio buttons are form input elements, not popup boxes.

JavaScript uses the equals sign (=) for variable assignment. For example: 'var x = 5;' assigns the value 5 to variable x. This is the standard assignment operator across programming languages.

The postfix increment operator a++ adds 1 to a and returns the original value (before increment). It is equivalent to a = a + 1. The increment happens after the value is used in the expression.

Wrapping code in a function prevents it from executing immediately when the page loads. Functions only run when explicitly called. This is essential for event handlers and code that should run on user interaction rather than page load.

Events are actions or occurrences that JavaScript can detect and respond to, such as clicks, key presses, mouse movements, and page loads. The browser triggers event handlers when these actions occur.

Cookies are small text files that websites store on a user's computer. They allow the webpage to persist data between sessions, such as login state, preferences, or shopping cart items. Cookies can be both written to and read from the user's browser.

JavaScript is a case-sensitive language. 'MyVar', 'myVar', and 'MYVAR' are three different variables. This applies to variable names, function names, keywords, and all identifiers in JavaScript code.

The onMouseOver event fires when the mouse pointer moves over an element. For links specifically, this event can be used to trigger actions like changing link appearance, showing tooltips, or prefetching content. JavaScript uses camelCase naming for events.

JavaScript strings are zero-indexed, meaning the first character is at position 0. The charAt() method returns the character at a specified index. To get the first character, use charAt(0). substring(1) would return from position 1 to the end.

The expression alert("hello +3+ times"); is a single valid string literal with no unescaped or unclosed quotes. The other options contain syntax errors because they have mismatched or unclosed double quotation marks inside the arguments.

The standard JavaScript method for opening a new browser window or tab is window.open(). Other options like window.launch() or popUp() are not built-in JavaScript window methods, and window.close() is used to close an existing window.

The indexOf() method searches for a substring within a string and returns the index of the first occurrence, or -1 if not found. The syntax is string.indexOf(substring). Options A and B use incorrect method names (substring, find), and option D incorrectly nests charAt(0) inside indexOf.

JavaScript code is embedded in HTML using the

document.write() is the correct JavaScript method to output text content to the HTML document. Option A is incomplete with a syntax error (missing opening quote), Option C uses ASP syntax (response.write), and Option D is just a string in parentheses without any command.

The

XSS defenses require preventing malicious script execution. Output encoding converts special characters to safe equivalents (e.g., < to <), blocking script injection. Data validation ensures input matches expected patterns before processing. HTTPS alone (options A and D) protects transmission but not XSS execution.