What’s the difference between event.preventDefault() and returning false in JavaScript?

The difference between event.preventDefault() and return false in JavaScript depends on how events are handled and whether you’re using vanilla JavaScript or jQuery. Below is a detailed breakdown with examples:

1. Core Differences

Action	event.preventDefault()	return false (Vanilla JS)	return false (jQuery)
Prevents Default	✅ (e.g., stops form submission, link navigation)	✅ (only in inline event handlers)	✅
Stops Propagation	❌ (event bubbles up the DOM)	❌ (in most browsers)	✅ (calls event.stopPropagation())
Works in	Vanilla JS, jQuery, frameworks	Inline HTML event handlers only	jQuery event handlers only

2. Vanilla JavaScript Examples

Example 1: Link Click (Inline Handler vs. addEventListener)

<!-- Inline HTML handler: return false prevents default -->
<a href="https://example.com" onclick="return false;">Inline Link</a>

<!-- addEventListener: return false has no effect -->
<a href="https://example.com" id="vanilla-link">Vanilla JS Link</a>
<script>
  document.getElementById("vanilla-link").addEventListener("click", (e) => {
    return false; // ❌ Does NOT prevent navigation
    e.preventDefault(); // ✅ Use this instead
  });
</script>

Example 2: Form Submission

// Vanilla JS: Prevent form submission but allow event bubbling
document.querySelector("form").addEventListener("submit", (e) => {
  e.preventDefault(); // ✅ Stops submission
  console.log("Form submitted (but not really)");
});

// Inline HTML: return false works
<form onsubmit="return false;">
  <button>Submit</button>
</form>

3. jQuery Examples

Example 3: Link Click in jQuery

// jQuery: return false prevents BOTH default and propagation
$("a").click(() => {
  console.log("Link clicked, but default and propagation stopped");
  return false; // = e.preventDefault() + e.stopPropagation()
});

// Compare to explicit methods:
$("a").click((e) => {
  e.preventDefault(); // Allow event to bubble
  e.stopPropagation(); // Stop bubbling (optional)
});

Example 4: Event Propagation

<div id="parent">
  <button id="child">Click Me</button>
</div>

<script>
  // Parent click handler
  $("#parent").click(() => {
    console.log("Parent clicked");
  });

  // Child click handler
  $("#child").click((e) => {
    console.log("Child clicked");
    return false; // ❗ Parent handler won't trigger
    // e.preventDefault(); // Parent handler WILL trigger
  });
</script>

4. Advanced Scenarios

Scenario 1: Nested Event Handlers

// Vanilla JS with addEventListener
document.querySelector("a").addEventListener("click", (e) => {
  e.preventDefault(); // Stop navigation
  console.log("First listener");
});

document.querySelector("a").addEventListener("click", (e) => {
  console.log("Second listener (still runs)"); // Bubbling continues
});

// With return false in jQuery:
$("a").click(() => {
  console.log("Only this listener runs");
  return false; // Prevents other listeners from firing
});

Scenario 2: Dynamic Actions

// Allow a link to navigate only if a condition is met
document.querySelector("a").addEventListener("click", (e) => {
  if (!userIsLoggedIn) {
    e.preventDefault(); // Block navigation
    alert("Please log in first!");
  }
});

5. Best Practices

1. Use preventDefault() in Vanilla JS:

• Explicit and clear intent.
• Works in all modern browsers and frameworks.

   element.addEventListener("click", (e) => {
     e.preventDefault(); // ✅ Recommended
   });

2. Avoid return false in Vanilla JS:

• Unreliable outside of inline handlers.
• Confusing behavior in addEventListener.

2. Use return false Sparingly in jQuery:

• Only when you need to stop both default and propagation.
• Prefer explicit methods for clarity:

$("#element").click((e) => {
  e.preventDefault(); // Stop default
  e.stopPropagation(); // Stop propagation (optional)
});

2. Avoid Stopping Propagation Unnecessarily:

• Event bubbling is useful for delegated events.
• Stopping propagation can break parent listeners.

Summary Table

Goal	Vanilla JS	jQuery
Prevent default action	e.preventDefault()	return false
Stop event bubbling	e.stopPropagation()	return false
Inline HTML event handlers	return false works	N/A
Modern code (frameworks like React/Vue)	e.preventDefault()	N/A (use framework methods)

Final Note

• Use preventDefault() for most vanilla JS/framework use cases.
• Use return false only in jQuery or legacy inline HTML handlers.
• Avoid mixing jQuery and vanilla JS event handling for consistency.