Eager (2.0)

Eager Gap Prevention (snapEagerness: 2.0)

Configuration: { snapEagerness: 2.0 }

This setting predicts two scroll steps ahead, making transitions more aggressive to virtually eliminate visual gaps.

🎯 When Aggressive Prevention is Needed

The 2.0 value is designed for scenarios where visual gaps are unacceptable:

• ✅ Virtually eliminates gaps: Even during very fast scrolling
• ✅ High-contrast headers: Where gaps would be very noticeable
• ✅ Complex header layouts: Multi-element headers that can't show partial states
• ✅ Mobile-heavy usage: Handles momentum scrolling aggressively
• ⚠️ More noticeable snapping: Movement feels less natural

🔍 How Two-Step Prediction Works

The algorithm looks further ahead to make earlier decisions:

const handleScroll = () => {
  const currentScrollY = window.scrollY;
  const elementRect = element.getBoundingClientRect();
  
  // Calculate current scroll velocity
  const scrollVelocity = currentScrollY - lastScrollY;
  
  // Predict TWO scroll steps ahead instead of one
  const predictedTop = elementRect.top - 2.0 * scrollVelocity;
  //                                      ↑
  //                        snapEagerness: 2.0 = predict 2 steps ahead
  
  // Switch to sticky much earlier in the scroll
  if (mode === 'relative' && predictedTop >= 0) {
    mode = 'sticky';
    element.style.position = 'sticky';
    element.style.top = '0';
  }
}

📐 The Mathematics of Eagerness

Understanding the prediction calculation:

• Current Position: elementRect.top - where the element is now
• Velocity: scrollVelocity - how fast we're scrolling
• Two-Step Prediction: currentPos - 2 * velocity - where we'll be in 2 frames
• Earlier Switching: Becomes sticky when prediction shows we're getting close

🚀 Ideal Use Cases

Consider snapEagerness: 2.0 when you need:

• Perfect visual consistency: Zero tolerance for any gaps
• High-contrast designs: Dark headers on light backgrounds where gaps stand out
• Complex header content: Multiple elements, images, or animations that can't show partial states
• Mobile-first applications: Momentum scrolling with unpredictable speeds
• Gaming or interactive interfaces: Where snappy behavior feels appropriate

⚖️ Trade-offs to Consider

The eager behavior comes with some trade-offs:

• Less natural movement: The prediction becomes noticeable to users
• Earlier transitions: May feel like the header is "jumping" to sticky mode
• Reduced connection to scroll: Movement feels slightly disconnected from user input
• Potential over-correction: May switch to sticky when it doesn't need to

🧪 Testing the Eager Behavior

Try these patterns to experience the aggressive gap prevention:

• Slow scrolling: Notice the earlier transition to sticky
• Medium speed: The snapping should be clearly noticeable
• Fast scrolling: Gaps should be completely eliminated
• Sudden stops: Try scrolling fast then suddenly stopping
• Direction reversals: Quick changes should be handled aggressively

📱 Mobile Performance

The 2.0 value is particularly effective on mobile devices:

• Handles the initial momentum burst of finger flicks
• Prevents gaps during the high-speed phase
• Maintains consistency during deceleration
• Works well with iOS and Android momentum algorithms

📊 Comparison with Other Values

Understanding the eagerness spectrum:

• snapEagerness: 0.0 - Pure natural (may show gaps)
• snapEagerness: 1.0 - Balanced default (subtle prediction)
• snapEagerness: 2.0 ← You are here (Aggressive gap prevention)
• snapEagerness: 3.0 - Intentional magnetic snapping

⚡ Performance Impact

The eager prediction has minimal performance cost:

• Same computational complexity: Still just a multiplication and comparison
• Earlier DOM updates: Transitions happen sooner but not more frequently
• Consistent frame rates: No additional processing per scroll event
• Memory usage identical: No additional state tracking required

Continue scrolling to see how the eager behavior handles different scroll patterns. Notice how the header seems more "decisive" about when to snap into position - it doesn't wait for the natural timing, but acts preemptively to ensure visual consistency.