CSS box model 📦

Get the CSS Box Model for a HTMLElement

This library is useful for when you need to obtain detailed positioning information about an element. Any time you are using Element.getBoundingClientRect() you might want to consider using css-box-model instead to get more detailed information.

Usage

// @flow
import { getBox } from 'css-box-model';

const el: HTMLElement = document.getElementById('foo');
const box: BoxModel = getBox(el);

// profit

Installation

yarn add css-box-model

The CSS Box Model

Box type	Composition
Margin box	margin + border + padding + content
Border box	border + padding + content
Padding box	padding + content
Content box	content

------------------------------------
|              MARGIN              |  (marginBox)
|  ------------------------------  |
|  |           BORDER           |  |  (borderBox)
|  |  ------------------------  |  |
|  |  |       PADDING        |  |  |  (paddingBox)
|  |  |  ------------------  |  |  |
|  |  |  |    CONTENT     |  |  |  |  (contentBox)
|  |  |  |                |  |  |  |
|  |  |  |                |  |  |  |
|  |  |  |                |  |  |  |
|  |  |  ------------------  |  |  |
|  |  |                      |  |  |
|  |  ------------------------  |  |
|  |                            |  |
|  ------------------------------  |
|                                  |
| ---------------------------------|

This our returned BoxModel:

export type BoxModel = {|
  // content + padding + border + margin
  marginBox: Rect,
  // content + padding + border
  borderBox: Rect,
  // content + padding
  paddingBox: Rect,
  // content
  contentBox: Rect,
  // for your own consumption
  border: Spacing,
  padding: Spacing,
  margin: Spacing,
|};

// Supporting types

// This is an extension of DOMRect and ClientRect
export type Rect = {|
  // ClientRect
  top: number,
  right: number,
  bottom: number,
  left: number,
  width: number,
  height: number,
  // DOMRect
  x: number,
  y: number,
  // Rect
  center: Position,
|};

export type Position = {|
  x: number,
  y: number,
|};

export type Spacing = {
  top: number,
  right: number,
  bottom: number,
  left: number,
};

API

getBox

(el: HTMLElement) => BoxModel

Use getBox to return the box model for an element

withScroll

(original: BoxModel, scroll?: Position = getWindowScroll()) => BoxModel

This is useful if you want to know the box model for an element relative to a page

const el: HTMLElement = document.getElementById('app');
const box: BoxModel = getBox(el);
const withScroll: BoxModel = withScroll(box);

You are welcome to pass in your own scroll. By default we we use the window scroll:

const getWindowScroll = (): Position => ({
  x: window.pageXOffset,
  y: window.pageYOffset,
});

calculateBox

(borderBox: AnyRectType, styles: CSSStyleDeclaration) => BoxModel

This will do the box model calculations without needing to read from the DOM. This is useful if you have already got a ClientRect and CSSStyleDeclaration as we do not need to recompute it.

const el: HTMLElement = document.getElementById('app');
const borderBox: ClientRect = el.getBoundingClientRect();
const styles: CSSStyleDeclaration = window.getComputedStyles(el);

const box: BoxModel = calculateBox(borderBox, styles);

AnyRectType allows for simple interoperability with any rect type

type AnyRectType = ClientRect | DOMRect | Rect | Spacing;