css-box-model 📦

Get accurate and well named CSS Box Model information about a Element.

Any time you are using Element.getBoundingClientRect() you might want to consider using css-box-model instead to get more detailed box model information.

Usage

// @flow
import { getBox } from 'css-box-model';
 
const el: HTMLElement = document.getElementById('foo');
const box: BoxModel = getBox(el);
 
// profit

Installation

## yarn 
yarn add css-box-model
 
# npm 
npm install css-box-model --save

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

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 / DOMRect and a CSSStyleDeclaration as then we can skip computing these values.

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;

createBox

({ borderBox, margin, border, padding }: CreateBoxArgs) => BoxModel

Allows you to create a BoxModel by passing in a Rect like shape (AnyRectType) and optionally your own margin, border and or padding.

type CreateBoxArgs = {|
  borderBox: AnyRectType,
  margin?: Spacing,
  border?: Spacing,
  padding?: Spacing,
|};

const borderBox: Spacing = {
  top: 10,
  right: 100,
  left: 20,
  bottom: 80,
};
const padding: Spacing = {
  top: 10,
  right: 20,
  left: 20,
  bottom: 10,
};
 
const box: BoxModel = createBox({ borderBox, padding });

Utility API

Functions to help you interact with the objects we provide

getRect

(spacing: AnyRectType) => Rect

Given any Rect like shape, return a Rect. Accepts any object that has top, right, bottom and right (eg ClientRect, DOMRect);

const spacing: Spacing = {
  top: 0,
  right: 100,
  bottom: 50,
  left: 50,
};
 
const rect: Rect = getRect(spacing);
 
console.log(rect);
 
/*
{
  top: 0,
  right: 100,
  bottom: 50,
  left: 50,
  width: 100,
  height: 50,
  x: 0,
  y: 0,
  center: { x: 50, y: 50 },
}
*/

expand

Used to expand a Spacing

(target: Spacing, expandBy: Spacing) => Spacing;

const original: Spacing = {
  top: 10,
  left: 11,
  right: 21,
  bottom: 22,
};
 
const expandBy: Spacing = {
  top: 1,
  left: 2,
  right: 3,
  bottom: 4,
};
 
const expanded: Spacing = expand(original, expandBy);
 
console.log(expanded);
 
/*
{
  // pulled back
  top: 8,
  left: 8
  // pushed forward
  bottom: 22,
  right: 22,
}
*/

shrink

Used to shrink a Spacing

(target: Spacing, shrinkBy: Spacing) => Spacing;

const original: Spacing = {
  top: 10,
  left: 10,
  right: 20,
  bottom: 20,
};
 
const shrinkBy: Spacing = {
  top: 2,
  left: 2,
  right: 2,
  bottom: 2,
};
 
const smaller: Spacing = shrink(original, shrinkBy);
 
console.log(smaller);
 
/*
{
  // pushed forward
  top: 12,
  left: 12
  // pulled back
  bottom: 18,
  right: 18,
}
*/