masonic

---

🧱 masonic

npm i masonic

---

A performant and versatile virtualized masonry grid for React based on Brian Vaughn's react-virtualized and further inspired by react-window.

Using Masonic, you're not just getting a component. You're getting the implementation details, as well, meaning advanced usage requiring little code is possible.

Features

• Easy to use It takes two minutes to start creating your own masonry grid with this component. For real, check out the demo on CodeSandbox.
• Blazing™ fast This component can seamlessly render tens of thousands of grid cells without lag via its virtualization algorithm and underlying data structures. For example, it uses a red black interval tree to determine which cells to render, based upon the scroll position and size of the window the grid is rendered in. Interval trees have O(log n + m) search performance 😱.
• TypeScript Intellisense and type safety mean fewer bugs in your implementation.
• Versatility All of <Masonry>'s implementation details (hooks, utilities) are exported, so you're not locked into to the default implementation. As you advance, it will be useful to have access to those internals. It's also possible to kick the virtualization out of the equation by providing an Infinity value to the overscanBy prop, though this would be a terrible idea for large lists.
• Autosizing The default <Masonry> component will automatically resize itself and its items if the content of the grid cells changes or resizes. For example, when an image lazily loads this component will automatically do the work of recalculating the size of that grid cell using @juggle/resize-observer. That said, you should try to premeasure things (including images) as often as possible in order to achieve the best user experience.

Quick Start

Check out the demo on CodeSandbox

import * as React from "react";
import { Masonry } from "masonic";

let i = 0;
const items = Array.from(Array(5000), () => ({ id: i++ }));

const EasyMasonryComponent = (props) => (
  <Masonry items={items} render={MasonryCard} />
);

const MasonryCard = ({ index, data: { id }, width }) => (
  <div>
    <div>Index: {index}</div>
    <pre>ID: {id}</pre>
    <div>Column width: {width}</div>
  </div>
);

Documentation

Components

Component	Description
<Masonry>	A "batteries included" masonry grid which includes all of the implementation details below. This component is the easiest way to get off and running in your app, before switching to more advanced implementations, if necessary. It will change its column count to fit its container's width and will decide how many rows to render based upon the height of the browser window.
<MasonryScroller>	A heavily-optimized component that updates useMasonry() when the scroll position of the browser window changes. This bare-metal component is used by <Masonry> above.
<List>	This is just a single-column <Masonry> component with no columnGutter prop, only rowGutter.

Hooks

Hook	Description
useMasonry()	This hook handles the render phases of the masonry layout and returns the grid as a React element.
usePositioner()	This hook creates the grid cell positioner and cache required by useMasonry(). This is the meat of the grid's layout algorithm, determining which cells to render at a given scroll position, as well as where to place new items in the grid.
useResizeObserver()	Creates a resize observer that forces updates to the grid when mutations are made to the grid cells affecting their size.
useContainerPosition()	A hook for measuring the width of the grid container, as well as its distance from the top of the document. These values are necessary to correctly calculate the number/width of columns to render, as well as the number of rows to render.
useScroller()	A hook for tracking whether the window is currently being scrolled and it's scroll position on the y-axis. These values are used for determining which grid cells to render and when to add styles to the grid container that maximize scroll performance.
useScrollToIndex()	A hook that creates a callback for scrolling to a specific index in the "items" array.
useInfiniteLoader()	A utility hook for seamlessly adding infinite scroll behavior to the useMasonry() hook. This hook invokes a callback each time the last rendered index surpasses the total number of items in your items array or the number defined in the totalItems option of this hook.

Utilities

Utility	Description
createPositioner()	Creates a cell positioner for the useMasonry() hook. The usePositioner() hook uses this utility under the hood.
createResizeObserver()	Creates a resize observer that fires an updater callback whenever the height of one or many cells change. The useResizeObserver() hook is using this under the hood.

Recipes

• Add infinite scrolling behavior to your Masonry component.
• Cells don't resize once they're measured? Build a Masonry grid without the resize observer.
• Reset <Masonry> layout when switching between routes within the same component.
  • Do the same with an advanced custom implementation using the usePositioner() hook.
• Render a Masonry component relative to a scrollable HTML element rather than the browser window.
• Add an isScrolling prop to cells

---

<Masonry>

An autosizing masonry grid that only renders items currently visible in the browser window. This component will change its column count to fit its container's width and will decide how many rows to render based upon the height of the browser window. To facilitate this, it uses useMasonry(), usePositioner(), useResizeObserver(),
useContainerPosition(), and useScroller() under the hood.

This is the "batteries included" option. It's the easiest way to get off and running with your app and a great stepping stone to more advanced implementations, should you need them.

Check out an example on CodeSandbox

import * as React from "react";
import { Masonry } from "masonic";

let i = 0;
const items = Array.from(Array(5000), () => ({ id: i++ }));

const EasyMasonryComponent = (props) => (
  <Masonry items={items} render={MasonryCard} />
);

const MasonryCard = ({ index, data: { id }, width }) => (
  <div>
    <div>Index: {index}</div>
    <pre>ID: {id}</pre>
    <div>Column width: {width}</div>
  </div>
);

Props

Required props

Prop	Type	Required?	Description
items	any[]	Yes	An array containing the data used by the grid items.
render	React.ComponentType<RenderComponentProps>	Yes	This component is rendered for each item of your items prop array. It should accept three props: index, width, and data. See RenderComponentProps for more detail on those props.

Column props

Props for tuning the column width, count, and gutter of your component.

Prop	Type	Default	Required?	Description
columnWidth	number	240	No	This is the minimum column width. Masonic will automatically size your columns to fill its container based on your provided columnWidth and columnGutter values. It will never render anything smaller than this defined width unless its container is smaller than its value.
columnGutter	number	0	No	This sets the horizontal space between grid columns in pixels. If rowGutter is not set, this also sets the vertical space between cells within a column in pixels.
rowGutter	number	Same as columnGutter	No	This sets the vertical space between cells within a column in pixels.
columnCount	number		No	By default, Masonic derives the column count from the columnWidth prop. However, in some situations it is nice to be able to override that behavior e.g. when creating a <List>.
maxColumnCount	number		No	Limits the number of columns used by Masonic. Useful for implementing responsive layouts.

Grid container props

These props customize how the grid container element is rendered.

Prop	Type	Default	Required?	Description
as	keyof JSX.IntrinsicElements | React.ComponentType<any>	"div"	No	This is the type of element the grid container will be rendered as.
id	string		No	Gives the grid container an id.
className	string		No	Gives the grid container a className.
style	React.CSSProperties		No	Adds extra style attributes to the container in addition to those created by the useMasonry() hook.
role	"grid" | "list"	"grid"	No	Optionally swap out the accessibility role prop of the container and its items.
tabIndex	number	0	No	Change the tabIndex of the grid container.

Grid item props

Props that customize how individual grid item containers are rendered.

Prop	Type	Default	Required?	Description
itemAs	keyof JSX.IntrinsicElements | React.ComponentType<any>	"div"	No	This is the type of element the grid items will be rendered as.
itemStyle	React.CSSProperties		No	Adds extra style attributes to the grid items in addition to those created by the useMasonry() hook.
itemHeightEstimate	number	300	No	This value is used for estimating the initial height of the masonry grid. It is important for the UX of the scrolling behavior and in determining how many items to render in a batch, so it's wise to set this value with some level accuracy, though it doesn't need to be perfect.
itemKey	(data: any, index: number) => string | number	(data, index) => index	No	The value returned here must be unique to the item. By default, the key is the item's index. This is ok if your collection of items is never modified. Setting this property ensures that the component in render is reused each time the masonry grid is reflowed. A common pattern would be to return the item's database ID here if there is one, e.g. data => data.id

Callbacks

Prop	Type	Default	Required?	Description
onRender	(startIndex: number, stopIndex: number, items: any[]) => void		No	This callback is invoked any time the items currently being rendered by the grid change. See onRender() arguments.

Other props

Prop	Type	Default	Required?	Description
overscanBy	number	2	No	This number is used for determining the number of grid cells outside of the visible window to render. The default value is 2 which means "render 2 windows worth (2 * height) of content before and after the items in the visible window". A value of 3 would be 3 windows worth of grid cells, so it's a linear relationship. Overscanning is important for preventing tearing when scrolling through items in the grid, but setting too high of a value may create too much work for React to handle, so it's best that you tune this value accordingly.
scrollToIndex	number | {index: number, align: "top" | "center" | "bottom"}		No	Scrolls to a given index within the grid. The grid will re-scroll any time the index changes.

onRender() arguments

Argument	Type	Description
startIndex	number	The index of the first item currently being rendered in the window
stopIndex	number	The index of the last item currently being rendered in the window
items	any[]	The array of items you provided to the items prop

RenderComponentProps

Prop	Type	Description
index	number	The index of the cell in the items prop array.
width	number	The rendered width of the cell's column.
data	any	The data at items[index] of your items prop array..

---

<MasonryScroller>

A heavily-optimized component that updates useMasonry() when the scroll position of the browser window changes. This bare-metal component is used by <Masonry> above.

When would you use this? If you're building an advanced masonry grid implementation, but you don't want to deal with figuring out how to optimize the exchange between scroll position changes in the browser window and the useMasonry() hook.

Check out an example on CodeSandbox

import * as React from "react";
import { MasonryScroller, usePositioner, useContainerPosition } from "masonic";
import { useWindowSize } from "@react-hook/window-size";

const MyMasonry = (props) => {
  const containerRef = React.useRef(null);
  const [windowWidth, windowHeight] = useWindowSize();
  const { offset, width } = useContainerPosition(containerRef, [
    windowWidth,
    windowHeight,
  ]);
  const positioner = usePositioner({ width, columnWidth: 320 });

  return (
    <MasonryScroller
      positioner={positioner}
      // The distance in px between the top of the document and the top of the
      // masonry grid container
      offset={offset}
      // The height of the virtualization window
      height={windowHeight}
      // Forwards the ref to the masonry container element
      containerRef={containerRef}
      {...props}
    />
  );
};

Props

In addition to these props, this component accepts all of the props outlined in <Masonry> with exception to columnGutter, rowGutter, columnWidth, columnCount, maxColumntCount, ssrWidth, and ssrHeight.

Prop	Type	Default	Required?	Description
offset	number	0	No	The vertical space in pixels between the top of the grid container and the top of the browser document.documentElement.
height	number		Yes	This is the height of the window. If you're rendering the grid relative to the browser window, the current document.documentElement.clientHeight is the value you'll want to set here. If you're rendering the grid inside of another HTML element, you'll want to provide the current element.offsetHeight here.
positioner	Positioner		Yes	A grid cell positioner and cache created by the usePositioner() hook or createPositioner() utility.
containerRef	React.MutableRefObject<HTMLElement | null>		No	Forwards a React ref to the grid container.
resizeObserver	ResizeObserver		No	A resize observer that tracks mutations to the grid cells and forces the Masonry grid to recalculate its layout if any cells affect column heights change. Check out the useResizeObserver() hook and createResizeObserver() utility.

---

<List>

This is a single-column <Masonry> component. That is, it uses the useMasonry() hook and other utilities to create a virtualized list.

Check out an example on CodeSandbox

import * as React from "react";
import { List } from "masonic";

let i = 0;
const items = Array.from(Array(5000), () => ({ id: i++ }));

const EasyListComponent = (props) => (
  <List items={items} rowGutter={32} render={ListCard} />
);

const ListCard = ({ index, data: { id }, width }) => (
  <div>
    <div>Index: {index}</div>
    <pre>ID: {id}</pre>
    <div>Column width: {width}</div>
  </div>
);

Props

In addition to these props, this component accepts all of the props outlined in <Masonry> with exception to columnGutter, columnWidth, columnCount, and maxColumnCount.

Prop	Type	Default	Required?	Description
rowGutter	number	0	No	The amount of vertical space in pixels to add between list item cards.

---

useMasonry(options)

This hook handles the render phases of the masonry layout and returns the grid as a React element.

Check out an example on CodeSandbox

import * as React from "react";
import { useWindowSize } from "@react-hook/window-size";
import {
  useMasonry,
  usePositioner,
  useContainerPosition,
  useScroller,
} from "masonic";

const MyMasonry = (props) => {
  const containerRef = React.useRef(null);
  const [windowWidth, height] = useWindowSize();
  const { offset, width } = useContainerPosition(containerRef, [
    windowWidth,
    height,
  ]);
  const { scrollTop, isScrolling } = useScroller(offset);
  const positioner = usePositioner({ width });

  return useMasonry({
    positioner,
    scrollTop,
    isScrolling,
    height,
    containerRef,
    ...props,
  });
};

Arguments

Argument	Type	Description
options	UseMasonryOptions	The distance in pixels between the top of your masonry container and the top of the document

UseMasonryOptions

Required options

Prop	Type	Required?	Description
items	any[]	Yes	An array containing the data used by the grid items.
positioner	Positioner	Yes	A grid cell positioner and cache created by the usePositioner() hook or createPositioner() utility.
height	number	Yes	This is the height of the window. If you're rendering the grid relative to the browser window, the current document.documentElement.clientHeight is the value you'll want to set here. If you're rendering the grid inside of another HTML element, you'll want to provide the current element.offsetHeight here.
scrollTop	number	Yes	The current scroll progress in pixel of the window the grid is rendered in. If you're rendering the grid relative to the browser window, you'll want the most current window.scrollY here. If you're rendering the grid inside of another HTML element, you'll want the current element.scrollTop value here. The useScroller() hook and <MasonryScroller> components will help you if you're rendering the grid relative to the browser window.
render	React.ComponentType<RenderComponentProps>	Yes	This component is rendered for each item of your items prop array. It should accept three props: index, width, and data. See RenderComponentProps.

Grid container options

Prop	Type	Default	Required?	Description
as	keyof JSX.IntrinsicElements | React.ComponentType<any>	"div"	No	This is the type of element the grid container will be rendered as.
id	string		No	Optionally gives the grid container an id prop.
className	string		No	Optionally gives the grid container a className prop.
style	React.CSSProperties		No	Adds extra style attributes to the container in addition to those created by the useMasonry() hook.
role	"grid" | "list"	"grid"	No	Optionally swap out the accessibility role prop of the container and its items.
tabIndex	number	0	No	Change the tabIndex of the grid container.
containerRef	React.MutableRefObject<HTMLElement | null>		No	Forwards a React ref to the grid container.

Grid item options

Prop	Type	Default	Required?	Description
itemAs	keyof JSX.IntrinsicElements | React.ComponentType<any>	"div"	No	This is the type of element the grid items will be rendered as.
itemStyle	React.CSSProperties		No	Adds extra style attributes to the grid items in addition to those created by the useMasonry() hook.
itemHeightEstimate	number	300	No	This value is used for estimating the initial height of the masonry grid. It is important for the UX of the scrolling behavior and in determining how many items to render in a batch, so it's wise to set this value with some level accuracy, though it doesn't need to be perfect.
itemKey	(data: any, index: number) => string | number	(data, index) => index	No	The value returned here must be unique to the item. By default, the key is the item's index. This is ok if your collection of items is never modified. Setting this property ensures that the component in render is reused each time the masonry grid is reflowed. A common pattern would be to return the item's database ID here if there is one, e.g. data => data.id

Callbacks

Prop	Type	Default	Required?	Description
onRender	(startIndex: number, stopIndex: number | undefined, items: any[]) => void		No	This callback is invoked any time the items currently being rendered by the grid change.

Other options

Prop	Type	Default	Required?	Description
overscanBy	number	2	No	This number is used for determining the number of grid cells outside of the visible window to render. The default value is 2 which means "render 2 windows worth (2 * height) of content before and after the items in the visible window". A value of 3 would be 3 windows worth of grid cells, so it's a linear relationship. Overscanning is important for preventing tearing when scrolling through items in the grid, but setting too high of a value may create too much work for React to handle, so it's best that you tune this value accordingly.
resizeObserver	ResizeObserver		No	A resize observer that tracks mutations to the grid cells and forces the Masonry grid to recalculate its layout if any cells affect column heights change. Check out the useResizeObserver() hook and createResizeObserver() utility.

---

usePositioner(options, deps?)

This hook creates the grid cell positioner and cache required by useMasonry(). This is the meat of the grid's layout algorithm, determining which cells to render at a given scroll position, as well as where to place new items in the grid.

Check out an example on CodeSandbox

import * as React from "react";
import { usePositioner, useContainerPosition, MasonryScroller } from "masonic";

const MyMasonry = ({ columnWidth = 300, columnGutter = 16, ...props }) => {
  const { width, offset } = useContainerPosition();
  const positioner = usePositioner({ width, columnWidth, columnGutter });
  return <MasonryScroller positioner={positioner} offset={offset} {...props} />;
};

Arguments

Argument	Type	Default	Required?	Description
options	UsePositionerOptions		Yes	Properties that determine the number of columns in the grid, as well as their widths.
deps	React.DependenciesList	[]	No	This hook will create a new positioner, clearing all existing cached positions, whenever the dependencies in this list change.

UsePositionerOptions

Argument	Type	Default	Required?	Description
width	number		Yes	The width of the container you're rendering the grid within, e.g. the container element's element.offsetWidth. That said, you can provide any width here.
columnWidth	number	200	No	The minimum column width. The usePositioner() hook will automatically size the columns to fill their container based upon the columnWidth and columnGutter values. It will never render anything smaller than this width unless its container itself is smaller than its value. This property has no effect if you're providing a columnCount.
columnGutter	number	0	No	This sets the horizontal space between grid columns in pixels. If rowGutter is not set, this also sets the vertical space between cells within a column in pixels.
rowGutter	number	Same as columnGutter	No	This sets the vertical space between cells within a column in pixels.
columnCount	number		No	By default, usePositioner() derives the column count from the columnWidth, columnGutter, and width props. However, in some situations it is nice to be able to override that behavior (e.g. creating a <List>-like component).
maxColumnCount	number		No	Limits the number of columns used by usePositioner(). Useful for implementing responsive layouts.

Returns a Positioner

Positioner

export interface Positioner {
  /**
   * The number of columns in the grid
   */
  columnCount: number;
  /**
   * The width of each column in the grid
   */
  columnWidth: number;
  /**
   * Sets the position for the cell at `index` based upon the cell's height
   */
  set: (index: number, height: number) => void;
  /**
   * Gets the `PositionerItem` for the cell at `index`
   */
  get: (index: number) => PositionerItem | undefined;
  /**
   * Updates cells based on their indexes and heights
   * positioner.update([index, height, index, height, index, height...])
   */
  update: (updates: number[]) => void;
  /**
   * Searches the interval tree for grid cells with a `top` value in
   * betwen `lo` and `hi` and invokes the callback for each item that
   * is discovered
   */
  range: (
    lo: number,
    hi: number,
    renderCallback: (index: number, left: number, top: number) => void
  ) => void;
  /**
   * Returns the number of grid cells in the cache
   */
  size: () => number;
  /**
   * Estimates the total height of the grid
   */
  estimateHeight: (itemCount: number, defaultItemHeight: number) => number;
  /**
   * Returns the height of the shortest column in the grid
   */
  shortestColumn: () => number;
  /**
   * Returns all `PositionerItem` items
   */
  all: () => PositionerItem[];
}

export interface PositionerItem {
  /**
   * This is how far from the top edge of the grid container in pixels the
   * item is placed
   */
  top: number;
  /**
   * This is how far from the left edge of the grid container in pixels the
   * item is placed
   */
  left: number;
  /**
   * This is the height of the grid cell
   */
  height: number;
  /**
   * This is the column number containing the grid cell
   */
  column: number;
}

---

useScroller(offset?, fps?)

A hook for tracking whether the window is currently being scrolled and it's scroll position on the y-axis. These values are used for determining which grid cells to render and when to add styles to the masonry container that maximize scroll performance.

Check out an example on CodeSandbox

import * as React from "react";
import { useMasonry, usePositioner, useScroller } from "masonic";

const MyMasonry = (props) => {
  const containerRef = React.useRef(null);
  const { offset, width } = useContainerPosition(containerRef);
  const positioner = usePositioner({ width });
  const { scrollTop, isScrolling } = useScroller(offset);

  return useMasonry({
    ...props,
    containerRef,
    positioner,
    scrollTop,
    isScrolling,
  });
};

Arguments

Argument	Type	Description
offset	number	The vertical space in pixels between the top of the grid container and the top of the browser document.documentElement.
fps	number	This determines how often (in frames per second) to update the scroll position of the browser window in state, and as a result the rate the masonry grid recalculates its visible cells. The default value of 12 has been very reasonable in my own testing, but if you have particularly heavy render components it may be prudent to reduce this number.

Returns {scrollTop: number; isScrolling: boolean}

---

useContainerPosition(elementRef, deps?)

A hook for measuring the width of the grid container, as well as its distance from the top of the document. These values are necessary to correctly calculate the number/width of columns to render, as well as the number of rows to render.

Check out an example on CodeSandbox

import * as React from "react";
import { useWindowSize } from "@react-hook/window-size";
import { useContainerPosition, MasonryScroller } from "masonic";

const MyMasonry = (props) => {
  const containerRef = React.useRef(null);
  const [windowWidth, windowHeight] = useWindowSize();
  const { offset, width } = useContainerRect(
    containerRef,
    // In this example, we want to recalculate the `offset` and `width`
    // any time the size of the window changes
    [windowWidth, windowHeight]
  );

  return (
    <MasonryScroller
      width={width}
      height={windowHeight}
      containerRef={containerRef}
      {...props}
    />
  );
};

Arguments

Argument	Type	Description
elementRef	number	A ref object created by React.useRef(). That ref should be provided to the containerRef property in useMasonry().
deps	React.DependenciesList	You can force this hook to recalculate the offset and width whenever this dependencies list changes. A common dependencies list might look like [windowWidth, windowHeight], which would force the hook to recalculate any time the size of the browser window changed.

Returns ContainerPosition

ContainerPosition

export interface ContainerPosition {
  /**
   * The distance in pixels between the top of the element in `elementRef` and the top of
   * the `document.documentElement`.
   */
  offset: number;
  /**
   * The `offsetWidth` of the element in `elementRef`.
   */
  width: number;
}

---

useScrollToIndex(positioner, options?)

A hook that creates a callback for scrolling to a specific index in the "items" array.

Check out an example on CodeSandbox

import * as React from "react";
import {
  useMasonry,
  usePositioner,
  useContainerPosition,
  useScroller,
  useScrollToIndex,
} from "masonic";

const MyMasonry = (props) => {
  const containerRef = React.useRef(null);
  const { offset, width } = useContainerPosition(containerRef);
  const { scrollTop, isScrolling } = useScroller(offset);
  const positioner = usePositioner({ width });
  const scrollToIndex = useScrollToIndex(positioner);

  React.useEffect(() => {
    if (props.scrollToIndex) {
      scrollToIndex(props.scrollToIndex);
    }
  }, [props.scrollToIndex, scrollToIndex]);

  return useMasonry({
    ...props,
    containerRef,
    positioner,
    scrollTop,
    isScrolling,
  });
};

Arguments

Argument	Type	Description
positioner	Positioner	A positioner created by the usePositioner() hook.
options	UseScrollToIndexOptions	Configuration options. See UseScrollToIndexOptions.

UseScrollToIndexOptions

Option	Type	Description
element	Window | HTMLElement | React.RefObject<HTMLElement> | null	The window element or a React ref for the window element. That is, this is the grid container.
align	"top" | "center" | "bottom"	Sets the vertical alignment of the cell within the grid container.
height	number	The height of the grid.
offset	number	The vertical space in pixels between the top of the grid container and the top of the window.

Returns (index: number) => void

---

useResizeObserver(positioner)

This hook creates a resize observer that forces updates to the grid cell positions when mutations are made to cells affecting their height.

Check out an example on CodeSandbox

import * as React from "react";
import { useMasonry, usePositioner, useResizeObserver } from "masonic";

const MyMasonry = (props) => {
  const positioner = usePositioner({ width: 1024 });
  const resizeObserver = useResizeObserver(positioner);

  return useMasonry({
    positioner,
    resizeObserver,
    scrollTop,
    isScrolling,
    height,
    ...props,
  });
};

Arguments

Argument	Type	Description
positioner	Positioner	The cell positioner created by the usePositioner() hook.

Returns a ResizeObserver

---

useInfiniteLoader(loadMoreItems, options?)

A utility hook for seamlessly adding infinite scroll behavior to the useMasonry() hook and the components that use it. This hook invokes a callback each time the last rendered index surpasses the total number of items in your items array or the number defined in the totalItems option.

Check out an example on CodeSandbox

import * as React from "react";
import { Masonry, useInfiniteLoader } from "masonic";

const InfiniteMasonry = (props) => {
  const [items, setItems] = useState([
    /* initial items */
  ]);
  const fetchMoreItems = async (startIndex, stopIndex, currentItems) => {
    const nextItems = await fetch(
      `/api/get-more?after=${startIndex}&limit=${startIndex + stopIndex}`
    );

    setItems((current) => [...current, ...nextItems]);
  };
  const maybeLoadMore = useInfiniteLoader(fetchMoreItems, {
    isItemLoaded: (index, items) => !!items[index],
  });

  return <Masonry {...props} items={items} onRender={maybeLoadMore} />;
};

Arguments

Argument	Type	Description
loadMoreItems	(startIndex: number, stopIndex: number, items: any[]) => any	This callback is invoked when more rows must be loaded. It will be used to determine when to refresh the list with the newly-loaded data.
options	UseInfiniteLoaderOptions	Configuration object for your loader, see UseInfiniteLoaderOptions below.

UseInfiniteLoaderOptions

Property	Type	Default	Description
isItemLoaded	(index: number, items: any[]) => boolean	(index, items) => items[index] !== undefined	A callback responsible for determining the loaded state of each item. Should return true if the item has already been loaded and false if not.
minimumBatchSize	number	16	The minimum number of new items to be loaded at a time. This property can be used to batch requests and reduce HTTP requests.
threshold	number	16	The threshold at which to pre-fetch data. A threshold X means that new data should start loading when a user scrolls within X cells of the end of your items array.
totalItems	number	9E9	The total number of items you'll need to eventually load (if known). This can be arbitrarily high if not known.

Returns (startIndex: number, stopIndex: number, items: any[]) => any

---

createPositioner(columnCount, columnWidth, columnGutter, rowGutter)

Creates a cell positioner for the useMasonry() hook. The usePositioner() hook uses this utility under the hood.

Arguments

Argument	Type	Description
columnCount	number	The number of columns in the grid
columnWidth	number	The width of each column in the grid
columnGutter	number	The amount of horizontal space between columns in pixels.
rowGutter	number	The amount of vertical space between cells within a column in pixels (falls back to columnGutter).
maxColumnCount	number	The upper bound of column count.

Returns Positioner

---

createResizeObserver(positioner, updater)

Creates a resize observer that forces updates to the grid cell positions when mutations are made to cells affecting their height.

Arguments

Argument	Type	Description
positioner	Positioner	A cell positioner created by the usePositioner() hook or the createPositioner() utility
updater	(updates: number[]) => void	A callback that fires whenever one or many cell heights change. Updates are provided to the callback in the form of a flat array: [index, height, index, height, index, height, ...]

Returns a ResizeObserver

---

Differences from react-virtualized

There are actually quite a few differences between these components and the originals, despite the overall design being highly inspired by them.

1. The react-virtualized component requires a <CellMeasurer>, cellPositioner, and cellMeasurerCache and a ton of custom implementation to get off the ground. It's very difficult to work with. In Masonic this functionality is built in using resize-observer-polyfill for tracking cell size changes.

2. This component can auto-calculate the number of columns to render based upon the defined columnWidth property. The column count will update any time it changes.

3. The algoirthm for updating cell positions and sizes is much more efficient in this component because only specific cells and columns are updated when cell sizes change, whereas in the original a complete reflow has to triggered.

4. The API and internals are a complete rewrite and because of the above points, is much easier to use in my opinion.

---

Legacy Documentation

• Version 2 documentation

LICENSE

MIT