Tech Notes

Understanding the DOM

Understanding the DOM

In this article, we will look at a fundamental aspect of working with web application testing, namely the DOM

When you start working in QA you may encounter a lot of different terms – test cases, selectors, CSS, XPATH, but what unites all these words is the so-called Document Object Model or DOM for short

What is the DOM?

Picture this: you open a web page. You see a headline, maybe a form, a big shiny button that says “Login.” It looks simple. But behind that clean design is a whole structure – a blueprint, if you will – and that’s the DOM

The browser takes the HTML written by developers and builds this structure. It’s organized like a tree:

  • Each element on the page (like a heading, paragraph, or button) becomes a node.
  • These nodes are nested within each other, creating a hierarchy.
  • That structure is what your browser — and your test scripts — rely on to make sense of the page.

Why Should QA Testers Care?

As a QA tester, especially in automation, your job often involves interacting with these elements. And your ability to do that well depends on how well you understand the DOM.

Here’s what the DOM lets you do:

  • Find elements to interact with – like a login button or input field.
  • Check if content is visible or correct – like verifying a success message.
  • Understand why something might not be working – like a button not responding or a field being hidden.

In short, the DOM is your map. Without it, you’re testing blind.

A Simple DOM Example

Let’s say this is the HTML for a basic login form:

<html>
  <body>
    <h1>Login</h1>
    <input type="text" id="username" />
    <button id="loginBtn">Login</button>
  </body>
</html>

The DOM representation of this is like a tree:

html
└── body
    ├── h1 ("Login")
    ├── input (id="username")
    └── button (id="loginBtn")

When your test scenario runs, it “walks” this tree to find and interact with elements. For example, this Python Selenium command:

driver.find_element(By.ID, "loginBtn").click()

is telling the browser: “Go to the DOM tree, find the button with the ID loginBtn, and click it.”

And that’s how automation works 🤫

Tips for exploring DOM

Start creating your DOM intuition by doing this:

  • Open any website, right-click, and choose “Inspect” in your web browser
  • Hover over the elements in the HTML panel and see how they highlight on the page
  • Practice identifying tags (<button>, <div>, <input>), attributes (id, class, name), and text content.

And the more time you spend here, the more second nature it becomes.

The DOM isn’t just for developers. It’s one of your most valuable tools as a QA tester. It helps you find bugs, write reliable tests, and understand how a page really works behind the scenes.

At Walltech, we help build strong, lasting QA skills – and it all starts with mastering the basics, like the DOM.

So go ahead. Open up DevTools. Get curious. Every great QA starts right here.

 

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