resize-observer-polyfill
Version:
A polyfill for the Resize Observer API
234 lines (203 loc) • 8.3 kB
JavaScript
import defineConfigurable from './defineConfigurable.js';
import getWindowOf from './getWindowOf.js';
import isBrowser from './isBrowser.js';
// Placeholder of an empty content rectangle.
const emptyRect = createRectInit(0, 0, 0, 0);
/**
* Converts provided string to a number.
*
* @param {number|string} value
* @returns {number}
*/
function toFloat(value) {
return parseFloat(value) || 0;
}
/**
* Extracts borders size from provided styles.
*
* @param {CSSStyleDeclaration} styles
* @param {...string} positions - Borders positions (top, right, ...)
* @returns {number}
*/
function getBordersSize(styles, ...positions) {
return positions.reduce((size, position) => {
const value = styles['border-' + position + '-width'];
return size + toFloat(value);
}, 0);
}
/**
* Extracts paddings sizes from provided styles.
*
* @param {CSSStyleDeclaration} styles
* @returns {Object} Paddings box.
*/
function getPaddings(styles) {
const positions = ['top', 'right', 'bottom', 'left'];
const paddings = {};
for (const position of positions) {
const value = styles['padding-' + position];
paddings[position] = toFloat(value);
}
return paddings;
}
/**
* Calculates content rectangle of provided SVG element.
*
* @param {SVGGraphicsElement} target - Element content rectangle of which needs
* to be calculated.
* @returns {DOMRectInit}
*/
function getSVGContentRect(target) {
const bbox = target.getBBox();
return createRectInit(0, 0, bbox.width, bbox.height);
}
/**
* Calculates content rectangle of provided HTMLElement.
*
* @param {HTMLElement} target - Element for which to calculate the content rectangle.
* @returns {DOMRectInit}
*/
function getHTMLElementContentRect(target) {
// Client width & height properties can't be
// used exclusively as they provide rounded values.
const {clientWidth, clientHeight} = target;
// By this condition we can catch all non-replaced inline, hidden and
// detached elements. Though elements with width & height properties less
// than 0.5 will be discarded as well.
//
// Without it we would need to implement separate methods for each of
// those cases and it's not possible to perform a precise and performance
// effective test for hidden elements. E.g. even jQuery's ':visible' filter
// gives wrong results for elements with width & height less than 0.5.
if (!clientWidth && !clientHeight) {
return emptyRect;
}
const styles = getWindowOf(target).getComputedStyle(target);
const paddings = getPaddings(styles);
const horizPad = paddings.left + paddings.right;
const vertPad = paddings.top + paddings.bottom;
// Computed styles of width & height are being used because they are the
// only dimensions available to JS that contain non-rounded values. It could
// be possible to utilize the getBoundingClientRect if only it's data wasn't
// affected by CSS transformations let alone paddings, borders and scroll bars.
let width = toFloat(styles.width),
height = toFloat(styles.height);
// Width & height include paddings and borders when the 'border-box' box
// model is applied (except for IE).
if (styles.boxSizing === 'border-box') {
// Following conditions are required to handle Internet Explorer which
// doesn't include paddings and borders to computed CSS dimensions.
//
// We can say that if CSS dimensions + paddings are equal to the "client"
// properties then it's either IE, and thus we don't need to subtract
// anything, or an element merely doesn't have paddings/borders styles.
if (Math.round(width + horizPad) !== clientWidth) {
width -= getBordersSize(styles, 'left', 'right') + horizPad;
}
if (Math.round(height + vertPad) !== clientHeight) {
height -= getBordersSize(styles, 'top', 'bottom') + vertPad;
}
}
// Following steps can't be applied to the document's root element as its
// client[Width/Height] properties represent viewport area of the window.
// Besides, it's as well not necessary as the <html> itself neither has
// rendered scroll bars nor it can be clipped.
if (!isDocumentElement(target)) {
// In some browsers (only in Firefox, actually) CSS width & height
// include scroll bars size which can be removed at this step as scroll
// bars are the only difference between rounded dimensions + paddings
// and "client" properties, though that is not always true in Chrome.
const vertScrollbar = Math.round(width + horizPad) - clientWidth;
const horizScrollbar = Math.round(height + vertPad) - clientHeight;
// Chrome has a rather weird rounding of "client" properties.
// E.g. for an element with content width of 314.2px it sometimes gives
// the client width of 315px and for the width of 314.7px it may give
// 314px. And it doesn't happen all the time. So just ignore this delta
// as a non-relevant.
if (Math.abs(vertScrollbar) !== 1) {
width -= vertScrollbar;
}
if (Math.abs(horizScrollbar) !== 1) {
height -= horizScrollbar;
}
}
return createRectInit(paddings.left, paddings.top, width, height);
}
/**
* Checks whether provided element is an instance of the SVGGraphicsElement.
*
* @param {Element} target - Element to be checked.
* @returns {boolean}
*/
const isSVGGraphicsElement = (() => {
// Some browsers, namely IE and Edge, don't have the SVGGraphicsElement
// interface.
if (typeof SVGGraphicsElement !== 'undefined') {
return target => target instanceof getWindowOf(target).SVGGraphicsElement;
}
// If it's so, then check that element is at least an instance of the
// SVGElement and that it has the "getBBox" method.
// eslint-disable-next-line no-extra-parens
return target => (
target instanceof getWindowOf(target).SVGElement &&
typeof target.getBBox === 'function'
);
})();
/**
* Checks whether provided element is a document element (<html>).
*
* @param {Element} target - Element to be checked.
* @returns {boolean}
*/
function isDocumentElement(target) {
return target === getWindowOf(target).document.documentElement;
}
/**
* Calculates an appropriate content rectangle for provided html or svg element.
*
* @param {Element} target - Element content rectangle of which needs to be calculated.
* @returns {DOMRectInit}
*/
export function getContentRect(target) {
if (!isBrowser) {
return emptyRect;
}
if (isSVGGraphicsElement(target)) {
return getSVGContentRect(target);
}
return getHTMLElementContentRect(target);
}
/**
* Creates rectangle with an interface of the DOMRectReadOnly.
* Spec: https://drafts.fxtf.org/geometry/#domrectreadonly
*
* @param {DOMRectInit} rectInit - Object with rectangle's x/y coordinates and dimensions.
* @returns {DOMRectReadOnly}
*/
export function createReadOnlyRect({x, y, width, height}) {
// If DOMRectReadOnly is available use it as a prototype for the rectangle.
const Constr = typeof DOMRectReadOnly !== 'undefined' ? DOMRectReadOnly : Object;
const rect = Object.create(Constr.prototype);
// Rectangle's properties are not writable and non-enumerable.
defineConfigurable(rect, {
x, y, width, height,
top: y,
right: x + width,
bottom: height + y,
left: x
});
return rect;
}
/**
* Creates DOMRectInit object based on the provided dimensions and the x/y coordinates.
* Spec: https://drafts.fxtf.org/geometry/#dictdef-domrectinit
*
* @param {number} x - X coordinate.
* @param {number} y - Y coordinate.
* @param {number} width - Rectangle's width.
* @param {number} height - Rectangle's height.
* @returns {DOMRectInit}
*/
export function createRectInit(x, y, width, height) {
return {x, y, width, height};
}