How to remove :hover css rule from stylesheet - javascript

I am working on a project based on jQuery and javascript. I am trying to add the CSS rules using javascript insert/addRule properties. What I want to do is :
I have to create hover effect and insert them into the stylesheet using javascript css properties. For this I am creating two classes for example:
.dummy {.... }
and
.dummy:hover{.....}
I want that If I change the hover effect then it must delete the previous one (or duplicates ) from the stylesheet and insert the new rules to the stylesheet.
But the problem is that If I try to remove or delete the CSS rules using deleteRule or removeRule it removes only
.dummy{...} rule but not the .dummy:hover{...}
Here is my code that can help you to understand what I am doing:
function createNewStyle() {
var style = document.createElement("style");
style.setAttribute('id', 'd-set-stylesheet');
style.appendChild(document.createTextNode(""));
document.head.appendChild(style);
} // this function might be not required but included here so that you may understand the program flow.
//the main issue is with this function.
function removeIfExists(class_name) {
var styleTag = document.getElementById("d-set-stylesheet");
var styleRef = styleTag.sheet ? styleTag.sheet : styleTag.styleSheet;
if (styleRef.rules) { //all browsers except IE 9-
console.log(styleRef);
for (var i in styleRef.cssRules) {
if (styleRef.cssRules[i].selectorText === "." + class_name+":hover" ||styleRef.cssRules[i].selectorText === "." + class_name )
styleRef.deleteRule(i);
}
} else {
var i;
for (i = 0; i < styleRef.rules.length; i++) {
//if(styleRef.rules[i].selectorText === "."+class_name || styleRef.rules[i].selectorText === "."+class_name+":hover")
styleRef.removeRule(i);
}
}
return styleRef;
}
//this function maybe not related with the issue but if it is you can check it.
function setNewClass(element, class_name, classSelector, styleObject) {
var stylesheet = removeIfExists(class_name);
if (element.data('hover-class') == null)
element.data('hover-class', class_name);
let count = 0;
var style = [];
var property = [{
"append": ":hover"
}, {
"append": ""
}];
for (j = 0; j < 2; j++) {
style.push({});
style[j].sheet = stylesheet;
style[j].selector = class_name;
style[j].type = classSelector;
style[j].property = property[j]["append"];
style[j].style = "";
}
for (i in styleObject) {
if (styleObject.hasOwnProperty(i))
if (count % 2 == 0)
style[0].style += styleObject[i] + ":";
else
style[0].style += styleObject[i] + ";";
count++;
}
style[1].style = "transition:" + styleObject.t_property_value;
addCSSRule(style);
}
function addCSSRule(styleSheet) {
console.log(styleSheet);
for (i = 0; i < styleSheet.length; i++)
if (styleSheet[i].sheet.insertRule)
styleSheet[i].sheet.insertRule(styleSheet[i].type + styleSheet[i].selector + styleSheet[i].property + "{" + styleSheet[i].style + "}", styleSheet[i].sheet.cssRules.length);
else
styleSheet[i].sheet.addRule(styleSheet[i].type + styleSheet[i].selector + styleSheet[i].property, styleSheet[i].sheet.style, -1);
}
Here are the images that of console.log
In the first image the hover and without hover class is added to CSS rules.
In the second image the previous hover class is not deleted while without hover class is deleted. I want hover transition must be deleted. Before adding new Rules to prevent duplication of classes and more than one transition on hovering the element should be prevented.
Thank you.

I found the answer today. I will explain it so that it can help others in future to understand the problem and solution.
As through my question, you can understand the issue. The problem was with this function only
function removeIfExists(class_name) {
......
if (styleRef.rules) { //all browsers except IE 9-
for (var i in styleRef.cssRules) {
.....
styleRef.deleteRule(i); //problem is with this.
.....
}
}
.......
return styleRef;
}
When I check the deleteRule on the basis of some test I found that when the deleteRule is called following things happens:
The css rule is deleted on the basis of index.
(The most important, as there is no documentation or clarification or explanation about this) The content get updated with their indexing. So that my function will no longer be able to delete the correct rules on the basis of old indexing.
To understand it better I will give you an example:
Suppose, I have added two rules in css such as: .dummy:hover{...} and .dummy{...}
Now the indexing of these rules will be as follows:
[0]: .dummy:hover rule
[1]: .dummy rule
When i call the delete rule what happen is :
// at i =0;
deleteRule(0);/* will be called and it will remove [0]: .dummy:hover rule
and then it will update the rules indexing again, which means
[1]: .dummy rule => [0]: .dummy rule */
// now when i = 1;
deleteRule(1); /* will be called and it will try to remove [1]: .dummy rule which is not here anymore and it will just skip the removal of [1]: .dummy rule.
So what I do to remove it is starting to remove the rule from highest indexing or in reverse order which means the i = 1 rule will be deleted first then i=0; rule so that there would not be any consequences.
and the function would changed as this:
function removeIfExists(class_name)
{
...
var styleRef = styleTag.sheet ? styleTag.sheet : styleTag.styleSheet;
var len = styleRef.cssRules ? styleRef.cssRules.length : styleRef.rules.length;
if(styleRef.rules){ //all browsers except IE 9-
for(i=len;i>0;i--)
{
if (styleRef.cssRules[i-1].selectorText === "." + class_name+":hover" ||styleRef.cssRules[i-1].selectorText === "." + class_name )
styleRef.deleteRule(i-1);
}
}
......
.....
}
return styleRef;
}
Note : The similar procedure would be followed for IE but I have not included it here.

Related

How to remove all jQuery validation engine classes from element?

I have a plugin that is cloning an input that may or may not have the jQuery validation engine bound to it.
so, it's classes may contain e.g. validate[required,custom[number],min[0.00],max[99999.99]] or any combination of the jQuery validation engine validators.
The only for sure thing is that the class begins with validate[ and ends with ], but to make it more complicated as in the example above, there can be nested sets of [].
So, my question is, how can I remove these classes (without knowing the full class) using jQuery?
Here is my implementation, It's not using regex, but meh, who said it had too?
//'first validate[ required, custom[number], min[0.00], max[99999.99] ] other another';
var testString = $('#test')[0].className;
function removeValidateClasses(classNames) {
var startPosition = classNames.indexOf("validate["),
openCount = 0,
closeCount = 0,
endPosition = 0;
if (startPosition === -1) {
return;
}
var stringStart = classNames.substring(0, startPosition),
remainingString = classNames.substring(startPosition),
remainingSplit = remainingString.split('');
for (var i = 0; i < remainingString.length; i++) {
endPosition++;
if (remainingString[i] === '[') {
openCount++;
} else if (remainingString[i] === ']') {
closeCount++;
if (openCount === closeCount) {
break;
}
}
}
//concat the strings, without the validation part
//replace any multi-spaces with a single space
//trim any start and end spaces
return (stringStart + remainingString.substring(endPosition))
.replace(/\s\s+/g, ' ')
.replace(/^\s+|\s+$/g, '');
}
$('#test')[0].className = removeValidateClasses(testString);
It might actually be simpler to do that without JQuery. Using the className attribute, you can then get the list of classes using split(), and check whether the class contains "validate[".
var classes = $('#test')[0].className.split(' ');
var newClasses = "";
for(var i = 0; i < classes.length; i++){
if(classes[i].indexOf('validate[') === -1){
newClasses += classes[i];
}
}
$('#test')[0].className = newClasses
I think this solution is even more simple. You just have to replace field_id with the id of that element and if the element has classes like some_class different_class validate[...] it will only remove the class with validate, leaving the others behind.
var that ='#"+field_id+"';
var classes = $(that).attr('class').split(' ');
$.each(classes, function(index, thisClass){
if (thisClass.indexOf('validate') !== -1) {
$(that).removeClass(classes[index])
}
});

Using javascript to reference current node?

So I'm doing a redesign for a site with an unhelpful CMS where I don't have full access to the markup (or ftp access). There's a node in particular which is hindering my progress significantly - its written with inline style & no class or ID and I have to change it (not remove it). Its looking like:
<div style="background-color: blue">
<div class="editablecontent">
(stuff I can edit in the CMS goes here)
</div>
</div>
I don't think getElementsByClassName is going to work here? but what sort of works is the very ugly defining an empty div with an ID then and document.getElementById.parentNode.parentNode.style.backgroundColor="white" which is obviously filthy and doesn't work in IE anyways and I need IE8 support (at least). I am not using a framework but do have access to the header.
Thanks in advance.
Assuming this content is unique in your document (e.g. there's only one of them), you can use this to find it:
function changeColor() {
var divs = document.getElementsByTagName("div");
for (var i = 0, len = divs.length; i < len; i++) {
if (divs[i].style.backgroundColor === "blue" &&
divs[i + 1] &&
divs[i + 1].parentNode === divs[i] &&
divs[i + 1].className === "editablecontent") {
divs[i].style.backgroundColor = "white";
return;
}
}
}
This does the following steps:
Get all divs in the document
Look for one with backgroundColor set to blue with an inline style setting
When you find one check to see if there is another div after it
If that next div is a child
If that next div has a className of "editablecontent"
Then, change its background color.
If you wanted any further checks based on other criteria to make sure you were finding the right object, you could add those to the logic, though these checks are all you have disclosed to us.
Working example: http://jsfiddle.net/jfriend00/NmxUn/
Another approach is to use getElementsByClassName and install a polyfill like this one to make it work in older browsers:
// Add a getElementsByClassName function if the browser doesn't have one
// Limitation: only works with one class name
// Copyright: Eike Send http://eike.se/nd
// License: MIT License
if (!document.getElementsByClassName) {
document.getElementsByClassName = function(search) {
var d = document, elements, pattern, i, results = [];
if (d.querySelectorAll) { // IE8
return d.querySelectorAll("." + search);
}
if (d.evaluate) { // IE6, IE7
pattern = ".//*[contains(concat(' ', #class, ' '), ' " + search + " ')]";
elements = d.evaluate(pattern, d, null, 0, null);
while ((i = elements.iterateNext())) {
results.push(i);
}
} else {
elements = d.getElementsByTagName("*");
pattern = new RegExp("(^|\\s)" + search + "(\\s|$)");
for (i = 0; i < elements.length; i++) {
if ( pattern.test(elements[i].className) ) {
results.push(elements[i]);
}
}
}
return results;
}
}
And, then you could simply do this, even on older versions of IE:
var items = document.getElementsByClassName("editablecontent");
if (items.length) {
items[0].parentNode.style.backgroundColor = "white";
}

Show/Hide image before filtering a table isn't working

I have web page with some really large tables that I'm filtering using some jquery routines I wrote. Anyway, when these tables get really large and the filtering functions can take some time to complete. So I figured I'd unhide a animated gif so the user had some feedback. However, the gif never appears when I call:
$('#loadingimg').show();
Unless I put an alert statement in front of it. I apologize for the ugly code, I'm not an experienced jquery/javascript programmer.
function filter()
{
var eles = ["mtmprogram","rate","stage"];
var tag;
var classes='';
$('#loadingimg').show();
//alert('hi');
$('.report').hide();
for (var i in eles)
{
tag = '#' + eles[i] + ' option:selected';
if ($(tag).val())
{
//$('.'+ $(tag).val()).show();
classes = classes + '.' + $(tag).val();
}
}
if (classes == '')
$('tr.report').show();
else
$(classes).show();
filterSubtables('Loan Number');
$('#loadingimg').hide();
}
Many thanks!
Maybe you aren't giving the #loadingimg element enough time to display. You could test this by running the rest of your code in a timeout:
function filter()
{
var eles = ["mtmprogram","rate","stage"],
classes = '';
$('#loadingimg').show();
//alert('hi');
setTimeout(function () {
$('.report').hide();
for (var i = 0, len = eles.length; i < len; i++)
{
var $tag = $('#' + eles[i] + ' option:selected');
if ($tag.val())
{
//$('.'+ $tag.val()).show();
classes = classes + '.' + $tag.val();
}
}
if (classes == '')
$('.report').show();
else
$(classes).show();
filterSubtables('Loan Number');
$('#loadingimg').hide();
}, 500);
}
Notice that I changed how the tag variable is used (this creates less CPU overhead to make less jQuery selections and to use as local a variable as possible). I also changed your loop to a better format that performs amazingly faster than for ( a in b ): http://jsperf.com/jquery-each-vs-for-loops/2

Select Element By CSS style (all with given style)

Is there a way to select all elements that have a given style using JavaScript?
Eg, I want all absolutely positioned elements on a page.
I would assume it is easier to find elements by style where the style is explicitly declared:
the style is non-inherited (such as positioning)
the style is not the default (as would be position:static).
Am I limited to those rules? Is there a better method for when those rules apply?
I would happily to use a selector engine if this is provided by one (ideally Slick - Mootools 1.3)
EDIT:
I came up with a solution that will only work with above rules.
It works by cycling through every style rule, and then selector on page.
Could anyone tell me if this is better that cycling through all elements (as recommended in all solutions).
I am aware that in IE I must change the style to lowercase, but that I could parse all styles at once using cssText. Left that out for simplicity.
Looking for best practice.
var classes = '';
Array.each(documents.stylesheets, function(sheet){
Array.each(sheet.rules || sheet.cssRules, function(rule){
if (rule.style.position == 'fixed') classes += rule.selectorText + ',';
});
});
var styleEls = $$(classes).combine($$('[style*=fixed]'));
You can keep Mootools, or whatever you use... :)
function getStyle(el, prop) {
var view = document.defaultView;
if (view && view.getComputedStyle) {
return view.getComputedStyle(el, null)[prop];
}
return el.currentStyle[prop];
}
​function getElementByStyle(style, value, tag)​ {
var all = document.getElementsByTagName(tag || "*");
var len = all.length;
var result = [];
for ( var i = 0; i < len; i++ ) {
if ( getStyle(all[i], style) === value )
result.push(all[i]);
}
return result;
}
For Mootools:
var styleEls = $$('*').filter(function(item) {
return item.getStyle('position') == 'absolute';
});
In jQuery you could use
$('*').filter( function(){
return ($(this).css('position') == 'absolute');
} );
[update]
Or even create a new selector.
got me interested and so here is one (its my 1st, so its not built for efficiency) to find elements by css property..
$.expr[':'].css = function(obj, index, meta, stack){
var params = meta[3].split(',');
return ($(obj).css(params[0]) == params[1]);
};
usage: $('optionalSelector:css(property,value)')
will return all elements (of optionalSelector) whose property = value
example: var visibleDivs = $('div:css(visibility,visible)');
will return all divs whose visibility is set to visible (works for the default visibility as well..)
There is no selector for CSS attributes, so you're pretty much stuck to looping through each element and checking it's position. Here's a jQuery method:
$("*").each(function() {
var pos = $(this).css('position');
if(pos == "absolute") {
// do something
}
else if (pos == "relative") {
// do something else
}
});
You can use Case statements instead of if/else as well.
Other than this solution, there is no selector per se that can search by CSS attributes (unless they were inline, maybe).

Find all CSS rules that apply to an element

Many tools/APIs provide ways of selecting elements of specific classes or IDs. There's also possible to inspect the raw stylesheets loaded by the browser.
However, for browsers to render an element, they'll compile all CSS rules (possibly from different stylesheet files) and apply it to the element. This is what you see with Firebug or the WebKit Inspector - the full CSS inheritance tree for an element.
How can I reproduce this feature in pure JavaScript without requiring additional browser plugins?
Perhaps an example can provide some clarification for what I'm looking for:
<style type="text/css">
p { color :red; }
#description { font-size: 20px; }
</style>
<p id="description">Lorem ipsum</p>
Here the p#description element have two CSS rules applied: a red color and a font size of 20 px.
I would like to find the source from where these computed CSS rules originate from (color comes the p rule and so on).
Since this question currently doesn't have a lightweight (non-library), cross-browser compatible answer, I'll try to provide one:
function css(el) {
var sheets = document.styleSheets, ret = [];
el.matches = el.matches || el.webkitMatchesSelector || el.mozMatchesSelector
|| el.msMatchesSelector || el.oMatchesSelector;
for (var i in sheets) {
var rules = sheets[i].rules || sheets[i].cssRules;
for (var r in rules) {
if (el.matches(rules[r].selectorText)) {
ret.push(rules[r].cssText);
}
}
}
return ret;
}
JSFiddle: http://jsfiddle.net/HP326/6/
Calling css(document.getElementById('elementId')) will return an array with an element for each CSS rule that matches the passed element.
If you want to find out more specific information about each rule, check out the CSSRule object documentation.
Short version12 April 2017
Challenger appears.
var getMatchedCSSRules = (el, css = el.ownerDocument.styleSheets) =>
[].concat(...[...css].map(s => [...s.cssRules||[]])) /* 1 */
.filter(r => el.matches(r.selectorText)); /* 2 */
Line /* 1 */ builds a flat array of all rules.
Line /* 2 */ discards non-matching rules.
Based on function css(el) by #S.B. on the same page.
Example 1
var div = iframedoc.querySelector("#myelement");
var rules = getMatchedCSSRules(div, iframedoc.styleSheets);
console.log(rules[0].parentStyleSheet.ownerNode, rules[0].cssText);
Example 2
var getMatchedCSSRules = (el, css = el.ownerDocument.styleSheets) =>
[].concat(...[...css].map(s => [...s.cssRules||[]]))
.filter(r => el.matches(r.selectorText));
function Go(big,show) {
var r = getMatchedCSSRules(big);
PrintInfo:
var f = (dd,rr,ee="\n") => dd + rr.cssText.slice(0,50) + ee;
show.value += "--------------- Rules: ----------------\n";
show.value += f("Rule 1: ", r[0]);
show.value += f("Rule 2: ", r[1]);
show.value += f("Inline: ", big.style);
show.value += f("Computed: ", getComputedStyle(big), "(…)\n");
show.value += "-------- Style element (HTML): --------\n";
show.value += r[0].parentStyleSheet.ownerNode.outerHTML;
}
Go(...document.querySelectorAll("#big,#show"));
.red {color: red;}
#big {font-size: 20px;}
<h3 id="big" class="red" style="margin: 0">Lorem ipsum</h3>
<textarea id="show" cols="70" rows="10"></textarea>
Shortcomings
No media handling, no #import, #media.
No access to styles loaded from cross-domain stylesheets.
No sorting by selector “specificity” (order of importance).
No styles inherited from parents.
May not work with old or rudimentary browsers.
Not sure how it copes with pseudo-classes and pseudo-selectors but seems to fare okay.
Maybe I will address these shortcomings one day.
Long version12 August 2018
Here’s a much more comprehensive implementation taken from someone’s GitHub page
(forked from this original code, via Bugzilla). Written for Gecko and IE, but is rumoured to work also with Blink.
4 May 2017: The specificity calculator has had critical bugs which I have now fixed. (I can’t notify the authors because I don’t have a GitHub account.)
12 August 2018: Recent Chrome updates seem to have decoupled object scope (this) from methods assigned to independent variables. Therefore invocation matcher(selector) has stopped working. Replacing it by matcher.call(el, selector) has solved it.
// polyfill window.getMatchedCSSRules() in FireFox 6+
if (typeof window.getMatchedCSSRules !== 'function') {
var ELEMENT_RE = /[\w-]+/g,
ID_RE = /#[\w-]+/g,
CLASS_RE = /\.[\w-]+/g,
ATTR_RE = /\[[^\]]+\]/g,
// :not() pseudo-class does not add to specificity, but its content does as if it was outside it
PSEUDO_CLASSES_RE = /\:(?!not)[\w-]+(\(.*\))?/g,
PSEUDO_ELEMENTS_RE = /\:\:?(after|before|first-letter|first-line|selection)/g;
// convert an array-like object to array
function toArray(list) {
return [].slice.call(list);
}
// handles extraction of `cssRules` as an `Array` from a stylesheet or something that behaves the same
function getSheetRules(stylesheet) {
var sheet_media = stylesheet.media && stylesheet.media.mediaText;
// if this sheet is disabled skip it
if ( stylesheet.disabled ) return [];
// if this sheet's media is specified and doesn't match the viewport then skip it
if ( sheet_media && sheet_media.length && ! window.matchMedia(sheet_media).matches ) return [];
// get the style rules of this sheet
return toArray(stylesheet.cssRules);
}
function _find(string, re) {
var matches = string.match(re);
return matches ? matches.length : 0;
}
// calculates the specificity of a given `selector`
function calculateScore(selector) {
var score = [0,0,0],
parts = selector.split(' '),
part, match;
//TODO: clean the ':not' part since the last ELEMENT_RE will pick it up
while (part = parts.shift(), typeof part == 'string') {
// find all pseudo-elements
match = _find(part, PSEUDO_ELEMENTS_RE);
score[2] += match;
// and remove them
match && (part = part.replace(PSEUDO_ELEMENTS_RE, ''));
// find all pseudo-classes
match = _find(part, PSEUDO_CLASSES_RE);
score[1] += match;
// and remove them
match && (part = part.replace(PSEUDO_CLASSES_RE, ''));
// find all attributes
match = _find(part, ATTR_RE);
score[1] += match;
// and remove them
match && (part = part.replace(ATTR_RE, ''));
// find all IDs
match = _find(part, ID_RE);
score[0] += match;
// and remove them
match && (part = part.replace(ID_RE, ''));
// find all classes
match = _find(part, CLASS_RE);
score[1] += match;
// and remove them
match && (part = part.replace(CLASS_RE, ''));
// find all elements
score[2] += _find(part, ELEMENT_RE);
}
return parseInt(score.join(''), 10);
}
// returns the heights possible specificity score an element can get from a give rule's selectorText
function getSpecificityScore(element, selector_text) {
var selectors = selector_text.split(','),
selector, score, result = 0;
while (selector = selectors.shift()) {
if (matchesSelector(element, selector)) {
score = calculateScore(selector);
result = score > result ? score : result;
}
}
return result;
}
function sortBySpecificity(element, rules) {
// comparing function that sorts CSSStyleRules according to specificity of their `selectorText`
function compareSpecificity (a, b) {
return getSpecificityScore(element, b.selectorText) - getSpecificityScore(element, a.selectorText);
}
return rules.sort(compareSpecificity);
}
// Find correct matchesSelector impl
function matchesSelector(el, selector) {
var matcher = el.matchesSelector || el.mozMatchesSelector ||
el.webkitMatchesSelector || el.oMatchesSelector || el.msMatchesSelector;
return matcher.call(el, selector);
}
//TODO: not supporting 2nd argument for selecting pseudo elements
//TODO: not supporting 3rd argument for checking author style sheets only
window.getMatchedCSSRules = function (element /*, pseudo, author_only*/) {
var style_sheets, sheet, sheet_media,
rules, rule,
result = [];
// get stylesheets and convert to a regular Array
style_sheets = toArray(window.document.styleSheets);
// assuming the browser hands us stylesheets in order of appearance
// we iterate them from the beginning to follow proper cascade order
while (sheet = style_sheets.shift()) {
// get the style rules of this sheet
rules = getSheetRules(sheet);
// loop the rules in order of appearance
while (rule = rules.shift()) {
// if this is an #import rule
if (rule.styleSheet) {
// insert the imported stylesheet's rules at the beginning of this stylesheet's rules
rules = getSheetRules(rule.styleSheet).concat(rules);
// and skip this rule
continue;
}
// if there's no stylesheet attribute BUT there IS a media attribute it's a media rule
else if (rule.media) {
// insert the contained rules of this media rule to the beginning of this stylesheet's rules
rules = getSheetRules(rule).concat(rules);
// and skip it
continue
}
// check if this element matches this rule's selector
if (matchesSelector(element, rule.selectorText)) {
// push the rule to the results set
result.push(rule);
}
}
}
// sort according to specificity
return sortBySpecificity(element, result);
};
}
Fixed bugs
= match → += match
return re ? re.length : 0; → return matches ? matches.length : 0;
_matchesSelector(element, selector) → matchesSelector(element, selector)
matcher(selector) → matcher.call(el, selector)
EDIT: This answer is now deprecated and no longer works in Chrome 64+. Leaving for historical context. In fact that bug report links back to this question for alternative solutions to using this.
Seems I managed to answer my own question after another hour of research.
It's as simple as this:
window.getMatchedCSSRules(document.getElementById("description"))
(Works in WebKit/Chrome, possibly others too)
Have a look at this library, which does what was asked for: http://www.brothercake.com/site/resources/scripts/cssutilities/
It works in all modern browsers right back to IE6, can give you rule and property collections like Firebug (in fact it's more accurate than Firebug), and can also calculate the relative or absolute specificity of any rule. The only caveat is that, although it understands static media types, it doesn't understand media-queries.
Here is my version of getMatchedCSSRules function which support #media query.
const getMatchedCSSRules = (el) => {
let rules = [...document.styleSheets]
rules = rules.filter(({ href }) => !href)
rules = rules.map((sheet) => [...(sheet.cssRules || sheet.rules || [])].map((rule) => {
if (rule instanceof CSSStyleRule) {
return [rule]
} else if (rule instanceof CSSMediaRule && window.matchMedia(rule.conditionText)) {
return [...rule.cssRules]
}
return []
}))
rules = rules.reduce((acc, rules) => acc.concat(...rules), [])
rules = rules.filter((rule) => el.matches(rule.selectorText))
rules = rules.map(({ style }) => style)
return rules
}
Here's a version of S.B.'s answer which also returns matching rules within matching media queries. I've removed the *.rules || *.cssRules coalescence and the .matches implementation finder; add a polyfill or add those lines back in if you need them.
This version also returns the CSSStyleRule objects rather than the rule text. I think this is a little more useful, since the specifics of the rules can be more easily probed programmatically this way.
Coffee:
getMatchedCSSRules = (element) ->
sheets = document.styleSheets
matching = []
loopRules = (rules) ->
for rule in rules
if rule instanceof CSSMediaRule
if window.matchMedia(rule.conditionText).matches
loopRules rule.cssRules
else if rule instanceof CSSStyleRule
if element.matches rule.selectorText
matching.push rule
return
loopRules sheet.cssRules for sheet in sheets
return matching
JS:
function getMatchedCSSRules(element) {
var i, len, matching = [], sheets = document.styleSheets;
function loopRules(rules) {
var i, len, rule;
for (i = 0, len = rules.length; i < len; i++) {
rule = rules[i];
if (rule instanceof CSSMediaRule) {
if (window.matchMedia(rule.conditionText).matches) {
loopRules(rule.cssRules);
}
} else if (rule instanceof CSSStyleRule) {
if (element.matches(rule.selectorText)) {
matching.push(rule);
}
}
}
};
for (i = 0, len = sheets.length; i < len; i++) {
loopRules(sheets[i].cssRules);
}
return matching;
}
var GetMatchedCSSRules = (elem, css = document.styleSheets) => Array.from(css)
.map(s => Array.from(s.cssRules).filter(r => elem.matches(r.selectorText)))
.reduce((a,b) => a.concat(b));
function Go(paragraph, print) {
var rules = GetMatchedCSSRules(paragraph);
PrintInfo:
print.value += "Rule 1: " + rules[0].cssText + "\n";
print.value += "Rule 2: " + rules[1].cssText + "\n\n";
print.value += rules[0].parentStyleSheet.ownerNode.outerHTML;
}
Go(document.getElementById("description"), document.getElementById("print"));
p {color: red;}
#description {font-size: 20px;}
<p id="description">Lorem ipsum</p>
<textarea id="print" cols="50" rows="12"></textarea>
Ensuring IE9+, I wrote a function which calculates CSS for requested element and its children, and gives possibility to save it to a new className if needed in snippet below.
/**
* #function getElementStyles
*
* Computes all CSS for requested HTMLElement and its child nodes and applies to dummy class
*
* #param {HTMLElement} element
* #param {string} className (optional)
* #param {string} extras (optional)
* #return {string} CSS Styles
*/
function getElementStyles(element, className, addOnCSS) {
if (element.nodeType !== 1) {
return;
}
var styles = '';
var children = element.getElementsByTagName('*');
className = className || '.' + element.className.replace(/^| /g, '.');
addOnCSS = addOnCSS || '';
styles += className + '{' + (window.getComputedStyle(element, null).cssText + addOnCSS) + '}';
for (var j = 0; j < children.length; j++) {
if (children[j].className) {
var childClassName = '.' + children[j].className.replace(/^| /g, '.');
styles += ' ' + className + '>' + childClassName +
'{' + window.getComputedStyle(children[j], null).cssText + '}';
}
}
return styles;
}
Usage
getElementStyles(document.getElementByClassName('.my-class'), '.dummy-class', 'width:100%;opaity:0.5;transform:scale(1.5);');
I think the answer from S.B. should be the accepted one at this point but it is not exact. It is mentioned a few times that there will be some rules that may be missed. Faced with that, I decided to use document.querySelectorAll instead of element.matches. The only thing is that you would need some kind of unique identification of elements to compare it to the one you are looking for. In most cases I think that is achievable by setting its id to have a unique value. That's how you can identify the matched element being yours. If you can think of a general way to match the result of document.querySelectorAll to the element you are looking for that would essentially be a complete polyfill of getMatchedCSSRules.
I checked the performance for document.querySelectorAll since it probably is slower than element.matches but in most cases it should not be a problem. I see that it takes about 0.001 milliseconds.
I also found CSSUtilities library that advertises that it can do this but I feel its old and has not been updated in a while. Looking at its source code, it makes me think there may be cases that it misses.
As the linked question is closed as a duplicate of this, I add an answer here instead.
The unanswered part 2: "Once I found the computed style, I want to know where it comes from"
By looping over the document.styleSheets, and looking at the getComputedStyle() before and after you modify it, you can detect what stylesheet is in use.
It's far from optimal, but at least it can detect if the rule you looking at is in use or not.
Here is an exemple:
<html><head>
<title>CSS Test</title>
<style id="style-a">
li {color: #333; font-size: 20px !important;}
li.bb {color: #600; font-size: 10px;}
p {margin: 5px;}
p {margin-bottom: 10px;}
</style>
<script>
window.addEventListener('DOMContentLoaded', async () => {
const selector = 'li';
// const selector = 'li.bb';
const exempleValues = {
'color': ['rgb(0, 0, 0)', 'rgb(255, 255, 255)'],
'font-size': ['10px', '12px'],
};
const delay = (t) => new Promise((k, e) => {setTimeout(k, t)});
for(const element of document.querySelectorAll(selector)) {
const elementCss = document.defaultView.getComputedStyle(element);
for(const sheet of document.styleSheets) {
for(const rule of sheet.cssRules) {
if(rule.selectorText !== selector) {
continue;
}
for(const properyName of rule.style) {
const currentValue = rule.style[properyName];
const priority = rule.style.getPropertyPriority(properyName)
if(!exempleValues[properyName]) {
console.warn('no exemple values for', properyName);
continue;
}
const exempleValue = exempleValues[properyName][exempleValues[properyName][0] === currentValue ? 1 : 0];
rule.style.setProperty(properyName, exempleValue, priority);
await delay(100);
if(exempleValue === elementCss[properyName]) {
console.log(selector, properyName, currentValue, priority || false, true, 'in use', element, sheet.ownerNode);
} else {
console.log(selector, properyName, currentValue, priority || false, false, 'overrided', element);
}
rule.style.setProperty(properyName, currentValue, priority);
await delay(100);
}
}
}
}
}, {once: true});
</script>
</head><body>
<h1>CSS Test</h1>
<p>html-file for testing css</p>
<ul>
<li>AAAA</li>
<li class="bb">BBBB</li>
<li>CCCC</li>
</ul>
</body></html>

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