In JavaScript, how can you access elements in the HTML document object model DOM to read or change them?

Introduction / Context:
Client side JavaScript interacts with web pages through the document object model, often shortened to DOM. To change text, attributes, styles, or structure, you must first locate the relevant elements in the DOM tree. This question checks whether you know the standard methods used to access elements so that scripts can read or update them.

Given Data / Assumptions:
- We are running JavaScript in a web browser.
- The DOM represents HTML elements as objects with properties and methods.
- JavaScript code needs to locate elements before changing them.
- Common methods include getElementById and querySelector.

Concept / Approach:
The DOM provides a rich API on the document object. Methods such as document.getElementById locate an element with a specific id, while document.getElementsByClassName returns a collection of elements with a given class. querySelector and querySelectorAll allow selection using CSS like selectors. Once an element is obtained, scripts can modify its textContent, attributes, or style. The correct answer must mention these DOM methods rather than unrelated tools like SQL or registry edits.

Step-by-Step Solution:
Step 1: Recall that document is the root object for DOM access in browser based JavaScript. Step 2: Remember key methods such as getElementById, getElementsByClassName, and querySelector. Step 3: Analyze the options and look for the one that names these DOM methods as the way to access elements. Step 4: Select that option as it correctly describes how scripts locate elements before modifying them.

Verification / Alternative check:
You can test this by opening a page with an element that has id main and running JavaScript in the browser console: document.getElementById("main").style.color = "red";. The element text changes color, confirming that DOM methods are used to access and modify elements. Reference materials and tutorials consistently introduce these methods as the standard way to work with the DOM.

Why Other Options Are Wrong:
Option B is wrong because SQL queries run against databases, not against DOM trees. Option C is incorrect as changing a file extension does not expose elements as variables. Option D is unrelated because operating system registry entries have nothing to do with DOM access. Option E is obviously not valid because printed pages cannot be manipulated by JavaScript.

Common Pitfalls:
A common pitfall is assuming that DOM queries are cheap and repeatedly calling them inside tight loops instead of caching references. Another issue is using getElementById for elements that do not exist, which results in null references and runtime errors. Developers should learn to choose the most appropriate DOM method and check for null before manipulating elements.

Final Answer:
JavaScript accesses DOM elements by calling methods on the document object, such as document.getElementById, document.getElementsByClassName, or document.querySelector, and then reading or changing the returned elements.