Real-world programming debugging walkthrough

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Real-world programming debugging walkthrough
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🐞 Real-World Bug: “Button Click Not Working

🔧 The Code:

html
<!DOCTYPE html>
<html>
<head>
<title>Button Bug</title>
</head>
<body>
<button id="clickMe">Click Me!</button>
<script>
document.getElementById("clickme").addEventListener("click", function() {
alert("Button clicked!");
});
</script>
</body>
</html>

🧠 Step-by-Step Debugging:

🔍 Step 1: Read the error

Open the browser console. You may see something like:

javascript
Uncaught TypeError: Cannot read properties of null (reading 'addEventListener')

🧩 Step 2: Reproduce the bug

Clicking the button does nothing. The alert doesn’t appear.

🔎 Step 3: Investigate

Check this line:

javascript
document.getElementById("clickme")

Now check the HTML:

html
<button id="clickMe">Click Me!</button>

🛑 Problem: ID is case-sensitive

  • clickme ≠ clickMe

✅ Step 4: Fix it

Update the code:

javascript
document.getElementById("clickMe").addEventListener("click", function() {
alert("Button clicked!");
});

Now clicking the button works. 🎉

🔄 Advanced Debug Tip: DOM Not Ready

If you moved the script to the head section or used defer=false, this can also cause the error.

Better Approach:

Wrap your code in DOMContentLoaded:

javascript
document.addEventListener("DOMContentLoaded", function() {
document.getElementById("clickMe").addEventListener("click", function() {
alert("Button clicked!");
});
});

💡 Key Lessons from This Debugging Example

Lesson Why It Matters
ID case sensitivity JavaScript is case-sensitive
DOM must be loaded Always access elements after they exist
Use console errors Always check browser dev tools
Small typo = Big bug Carefully check spelling & IDs

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