event.preventDefault() vs return false: Complete Guide

event.preventDefault() and return false both prevent default browser behavior but differ significantly in their approach and scope. preventDefault() is a method that explicitly stops the default action while allowing event propagation to continue, whereas return false in jQuery context prevents both the default action and stops event propagation completely. The choice between them depends on your specific needs - whether you want to allow other handlers to potentially run (preventDefault()) or completely halt the event flow (return false).

Contents

• Core Differences Between event.preventDefault() and return false
• Behavior in Plain JavaScript vs jQuery
• When to Use Each Method
• Error Handling and Reliability
• Performance Considerations
• Best Practices and Recommendations

Core Differences Between event.preventDefault() and return false

The fundamental distinction lies in what each method actually does when executed during event handling:

event.preventDefault()

• Only prevents the browser’s default action associated with the event
• Allows event propagation to continue to parent elements
• Is explicit and requires access to the event object
• Must be called on the event object (e.preventDefault())

return false

• In jQuery context: prevents default action AND stops event propagation
• In vanilla JavaScript: behavior varies depending on how the handler is attached
• Implicit - returns from the handler function
• Doesn’t require explicit event object access

Key Insight: As explained in the CSS-Tricks article, “jQuery handles return false as an internal flag — using it to mean ‘prevent default and stop propagation’.” This is crucial for understanding why the same code behaves differently in different contexts.

Behavior in Plain JavaScript vs jQuery

The behavior of return false varies significantly depending on the JavaScript environment:

jQuery Event Handlers

In jQuery, return false from an event handler automatically calls both preventDefault() and stopPropagation():

// In jQuery - return false does both
$('a').click(function(e) {
    // Custom logic here
    return false; // Prevents default navigation AND stops bubbling
});

This makes return false convenient but potentially confusing because it does more than its name suggests.

Plain JavaScript (addEventListener)

With modern addEventListener(), return false does nothing at all:

// Vanilla JS - return false has no effect
document.querySelector('a').addEventListener('click', function(e) {
    return false; // Does NOT prevent default navigation
});

DOM0 Event Handlers (Inline)

For inline event handlers, return false only works if properly included:

<!-- This works -->
<a href="#" onclick="return false;">Link</a>

<!-- This doesn't work -->
<a href="#" onclick="false;">Link</a>

As Stack Overflow explains, “return false from a DOM2 handler (addEventListener) does nothing at all… from a DOM0 handler (onclick=“return …”), it prevents the default (provided you include the return in the attribute) but not bubbling.”

When to Use Each Method

Use event.preventDefault() When:

1. You need explicit control over preventing default behavior while allowing propagation
2. Working with modern JavaScript and addEventListener()
3. You want consistent behavior across different JavaScript libraries
4. Multiple handlers need to run on the same event
5. You need conditional prevention based on runtime logic

// Example: Only prevent default if validation fails
function handleFormSubmit(e) {
    if (!validateForm()) {
        e.preventDefault(); // Only prevent when needed
    }
}

Use return false When:

1. Working exclusively with jQuery and want convenience
2. You need to stop both default behavior AND propagation
3. You want concise syntax in simple event handlers
4. Maintaining legacy jQuery code

// jQuery-specific usage
$('form').submit(function() {
    if (!validateForm()) {
        return false; // Prevents submission AND stops propagation
    }
});

Error Handling and Reliability

This is a critical consideration that many developers overlook:

event.preventDefault() Reliability

• More robust against errors
• If an exception occurs before preventDefault(), the default behavior may still execute
• Explicit method call is less likely to be accidentally skipped

return false Vulnerability

• If any code before return false throws an error, the return statement never executes
• This means the default behavior will occur unexpectedly

As noted in the Wikitechy tutorial, “if some exception raised in the handler then the return false statement will be skipped and the behavior will be opposite to what we want.”

Example of the problem:

// Problematic with return false
$('a').click(function() {
    someFunctionThatMightThrow(); // If this fails, return false never executes
    return false;
});

// More reliable with preventDefault
$('a').click(function(e) {
    try {
        someFunctionThatMightThrow();
        e.preventDefault();
    } catch (error) {
        e.preventDefault(); // Still prevent default even if error occurs
    }
});

Performance Considerations

While both methods have similar performance characteristics, there are some nuances:

Execution Speed

• preventDefault() is typically marginally faster as it’s a direct method call
• return false involves function return handling which has slight overhead
• In most applications, this difference is negligible

Memory Usage

• preventDefault() requires the event object to be passed and maintained
• return false doesn’t require this, but the difference is minimal

Bundle Size

• Using preventDefault() is more library-agnostic
• If you’re using jQuery, return false might be slightly more optimized internally

The SQLpey article concludes that “prefer event.preventDefault() for clarity and reliability, especially in complex event handling scenarios.”

Best Practices and Recommendations

Modern JavaScript Development

Recommendation: Always prefer event.preventDefault() in modern applications:

// Modern approach - explicit and reliable
document.addEventListener('click', function(e) {
    if (shouldPreventDefault(e.target)) {
        e.preventDefault();
    }
});

jQuery Applications

Recommendation: Use preventDefault() even in jQuery for better maintainability:

// Better jQuery practice
$('a').click(function(e) {
    // Custom logic
    e.preventDefault(); // More explicit than return false
});

Legacy Codebases

If maintaining legacy jQuery code that uses return false, ensure proper error handling:

// Safer legacy pattern
$('form').submit(function(e) {
    try {
        if (!validateForm()) {
            return false;
        }
    } catch (error) {
        e.preventDefault(); // Fallback
        console.error('Form submission error:', error);
    }
});

Code Style Guidelines

1. Be explicit: preventDefault() clearly states intent
2. Handle errors: Always wrap return false in try-catch blocks
3. Document behavior: Comment when using return false to explain it stops propagation
4. Consistency: Choose one approach and stick to it throughout your codebase

Conclusion

Key Takeaways

1. Fundamental difference: preventDefault() only stops default behavior, while return false in jQuery stops both default behavior and propagation
2. Context matters: return false behaves differently in vanilla JS vs jQuery vs inline handlers
3. Reliability: preventDefault() is more robust against JavaScript errors
4. Explicitness: preventDefault() clearly communicates your intent

Practical Recommendations

• For new projects: Use event.preventDefault() exclusively for consistency and reliability
• For jQuery projects: Still prefer preventDefault() unless you specifically need to stop propagation
• For legacy code: Add error handling around return false statements
• For team collaboration: Establish clear guidelines on which method to use

Final Thought

As the SourceBae blog suggests, “Choosing between event.preventDefault() and return false is based on your individual requirements.” However, in most modern development scenarios, the explicit and reliable nature of preventDefault() makes it the superior choice for preventing default event behavior in JavaScript applications.

Sources

1. The difference between ‘return false;’ and ‘e.preventDefault();’ | CSS-Tricks
2. javascript - event.preventDefault() vs. return false - Stack Overflow
3. javascript - When to use PreventDefault( ) vs Return false? - Stack Overflow
4. Event.preventDefault() vs. return false - SourceBae
5. javascript tutorial - Event.preventDefault() Vs. return false - Wikitechy
6. Top Methods to Prevent Default Events in JavaScript - SQLpey
7. DOM events: stopPropagation vs preventDefault() vs. return false - Flavio Copes
8. When to use PreventDefault() vs Return false in JavaScript ? - GeeksforGeeks
9. Difference Between event.preventDefault() and return false in jQuery - Tutorialspoint
10. How to correctly use preventDefault(), stopPropagation(), or return false; on Events - Medium