ng-if vs. ng-show/ng-hide performance issue

Both ng-if and ng-show/ng-hide are used for conditionally displaying elements in AngularJS, but they have different behaviors and impact performance in different ways.

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1. Key Differences Between ng-if and ng-show/ng-hide

Feature	ng-if	ng-show / ng-hide
DOM Manipulation	Adds/removes elements from the DOM	Only changes the display CSS property (keeps the element in the DOM)
Performance Impact	Higher impact if used frequently (DOM re-creation)	Lower impact since elements remain in the DOM
Scope Handling	Scope is destroyed and recreated	Scope remains active
Use Case	Best for elements that appear/disappear infrequently	Best for toggling visibility without destroying data

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2. Performance Considerations

ng-if (Better for Memory Usage)

• Removes and re-creates elements from the DOM when the condition changes.
• When an element is removed, its child elements, bindings, and watchers are destroyed.
• Helps reduce memory usage when elements are no longer needed.
• Performance Issue: Frequent toggling leads to unnecessary re-creation of elements, causing lag.

Example:

<div ng-if="isVisible">
    <h2>This element is created only when `isVisible` is true.</h2>
</div>

When to Use ng-if?

• When an element should be completely removed from the DOM when not needed.
• When reducing memory consumption is a priority.
• When dealing with large data sets or complex UI elements that should not persist when hidden.

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ng-show / ng-hide (Better for UI Performance)

• Only modifies CSS (display: none;), so the element remains in the DOM.
• The scope and event listeners remain active, reducing DOM manipulation.
• Performance Issue: More watchers remain active, leading to increased CPU usage if used on too many elements.

Example:

<div ng-show="isVisible">
    <h2>This element remains in the DOM but is hidden when `isVisible` is false.</h2>
</div>

When to Use ng-show / ng-hide?

• When you need to frequently toggle visibility without destroying the element.
• When elements contain input fields, animations, or data that should not be lost when hidden.
• When performance is more about reducing DOM re-renders rather than memory usage.

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3. Performance Benchmarks: When to Choose What?

Scenario	Use ng-if	Use ng-show/ng-hide
Rendering large lists	(prevents unnecessary memory usage)	(keeps hidden elements in memory)
Frequently toggling elements	(high DOM manipulation overhead)	(no re-creation, just toggles visibility)
Forms with input fields	(destroys data and input fields)	(keeps user inputs intact)
Modal pop-ups	(destroys and recreates modal for better memory management)	(if keeping form inputs and animations)
Navigation menus	(if menu is rarely used)	(if toggled often)

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4. Best Practices for Optimizing Performance

Use ng-if for heavy UI elements that are rarely shown.
Use ng-show/ng-hide for UI elements that toggle frequently but should remain in memory.
Minimize the number of watchers by combining conditions in a controller.
Use track by in ng-repeat to optimize re-renders if ng-if is used inside loops.
Consider lazy loading for large components instead of keeping them hidden.

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Final Verdict

• Use ng-if when you want to reduce memory usage by destroying elements when not needed.
• Use ng-show/ng-hide when you want better UI performance by keeping elements in memory.

Let me know if you need more details!