cjm-fasthtml-virtual-scrollbar

Install

pip install cjm_fasthtml_virtual_scrollbar

Project Structure

nbs/
├── components/ (1)
│   └── scrollbar.ipynb  # Custom scrollbar component with proportional thumb for position indication.
├── core/ (2)
│   ├── math.ipynb    # Pure math functions for scrollbar thumb position and size calculation.
│   └── models.ipynb  # Data models for scrollbar configuration, state, and HTML ID generation.
└── js/ (1)
    └── scrollbar.ipynb  # JavaScript generator for custom scrollbar interaction (drag thumb, click track, position sync).

Total: 4 notebooks across 3 directories

Module Dependencies

graph LR
    components_scrollbar[components.scrollbar<br/>scrollbar]
    core_math[core.math<br/>math]
    core_models[core.models<br/>models]
    js_scrollbar[js.scrollbar<br/>scrollbar]

    components_scrollbar --> core_math
    components_scrollbar --> core_models
    js_scrollbar --> core_models

3 cross-module dependencies detected

CLI Reference

No CLI commands found in this project.

Module Overview

Detailed documentation for each module in the project:

math (math.ipynb)

Pure math functions for scrollbar thumb position and size calculation.

Import

from cjm_fasthtml_virtual_scrollbar.core.math import (
    compute_scrollbar
)

Functions

def compute_scrollbar(position: int,           # Current position (0-indexed)
                      visible_count: int,       # Number of visible items
                      total_items: int,          # Total item count
                      track_height: float,       # Scrollbar track height in px
                      min_thumb_height: int = 24,  # Minimum thumb height in px
                      max_position: Optional[int] = None,  # Upper bound of position range (None = total_items - visible_count)
                      thumb_ratio: Optional[float] = None,  # Thumb height as fraction of track (None = visible_count / total_items)
                     ) -> Tuple[float, float]:   # (thumb_top_percent, thumb_height_percent)
    """
    Compute scrollbar thumb position and size as percentages.
    
    When thumb_ratio and max_position are explicitly provided (cursor-based
    model), the thumb size and range are fully determined by those values
    regardless of the visible_count vs total_items relationship.
    """

models (models.ipynb)

Data models for scrollbar configuration, state, and HTML ID generation.

Import

from cjm_fasthtml_virtual_scrollbar.core.models import (
    ScrollbarConfig,
    ScrollbarState,
    ScrollbarIds
)

Classes

@dataclass
class ScrollbarConfig:
    "Initialization-time configuration for a virtual scrollbar."
    
    prefix: str = 'sb'  # HTML ID prefix
    show_scrollbar: bool = True  # Enable/disable scrollbar rendering
    min_thumb_height: int = 24  # Minimum thumb height in pixels
    track_width: int = 3  # Track width in Tailwind units (w-3 = 12px)
    auto_hide: bool = True  # Hide when total_items <= visible_count

@dataclass
class ScrollbarState:
    "Mutable runtime state for a virtual scrollbar."
    
    position: int = 0  # Current position (0-indexed)
    visible_count: int = 1  # Number of visible items
    total_items: int = 0  # Total item count
    max_position: Optional[int]  # Upper bound of position range (None = total_items - visible_count)
    thumb_ratio: Optional[float]  # Thumb height as fraction of track (None = visible_count / total_items)

@dataclass
class ScrollbarIds:
    "HTML element ID generators for a scrollbar instance."
    
    prefix: str = 'sb'  # Instance prefix
    
    def track(self) -> str: return f"{self.prefix}-scrollbar-track"  # Scrollbar track container
    
        @property
        def thumb(self) -> str: return f"{self.prefix}-scrollbar-thumb"  # Draggable thumb element
    
    def thumb(self) -> str: return f"{self.prefix}-scrollbar-thumb"  # Draggable thumb element

scrollbar (scrollbar.ipynb)

Custom scrollbar component with proportional thumb for position indication.

Import

from cjm_fasthtml_virtual_scrollbar.components.scrollbar import (
    render_scrollbar_thumb,
    render_scrollbar
)

Functions

def render_scrollbar_thumb(
    state: ScrollbarState,       # Scrollbar state
    config: ScrollbarConfig,     # Scrollbar config
    ids: ScrollbarIds,           # HTML IDs
    track_height: float = 600.0, # Track height for min thumb calculation
    oob: bool = False,           # Whether to include hx-swap-oob
) -> Div:  # Thumb element
    "Render the scrollbar thumb at the correct position."

def _build_track_cls(track_width: int) -> str:  # Combined CSS class string
    "Build track CSS classes for a given width."

def render_scrollbar(
    state: ScrollbarState,       # Scrollbar state
    config: ScrollbarConfig,     # Scrollbar config
    ids: ScrollbarIds,           # HTML IDs
) -> Div:  # Complete scrollbar (track + thumb)
    "Render the custom scrollbar with track and proportional thumb."

scrollbar (scrollbar.ipynb)

JavaScript generator for custom scrollbar interaction (drag thumb, click track, position sync).

Import

from cjm_fasthtml_virtual_scrollbar.js.scrollbar import (
    generate_scrollbar_js
)

Functions

def generate_scrollbar_js(
    ids: ScrollbarIds,           # Scrollbar HTML IDs (track, thumb)
    position_input_id: str,      # ID of hidden input (kept for API compat, not used for position sync)
    nav_url: str,                # URL to POST target index to
    nav_param: str = "target_index",  # Parameter name for the index value
    on_interact: str = "",       # JS callback name, called on user interaction start (drag/click)
) -> str:  # JavaScript IIFE code fragment
    "Generate JS for scrollbar: thumb positioning from track data + drag/click interaction."