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I am trying to move an element from the light DOM to the shadow DOM, but when I do so the styling isn't copying over. I tried to fix this by setting the newElement.style = window.getComputedStyle(elem), but this hasn't seemed to work. The styles should be:
.card {
color: #ff0;
font-size: 3rem;
font-weight: 600;
border: 3px solid blueviolet;
background-color: greenyellow;
}
but the styles don't apply and when I print the getComputedStyle() to console what I see is:
all the values are empty
However, when I loop through the properties of getComputedStyle() with .getPropertyValue() like so:
for(let property of style){
console.log(`property: ${property}, value: ${style.getPropertyValue(property)}`);
}
what I get in the console is:
the correct values
So I'm confused as to why getComputedStyle() doesn't contain the values, but using getComputedStyle().getPropertyValue() returns the correct values. I'm sure I'm missing something obvious, as I couldn't find another post about this anywhere.
Any help would be greatly appreciated, thanks in advance.
EDIT: I've taken the code provided by Danny below and modified it to better show the issue I'm facing:
<style>
.card {
color: yellow;
background: green;
}
</style>
<my-element>
<div class="card">lightDOM reflected to shadowDOM</div>
</my-element>
<script>
customElements.define("my-element", class extends HTMLElement {
constructor(){
super().attachShadow({mode:"open"}).innerHTML = ``;
}
connectedCallback() {
setTimeout(() => { // wait till innerHTML is parsed
let card = this.children[0]; // Get the light DOM Card element
this.shadowRoot.appendChild(card.cloneNode(true)); // Append it to the shadowDOM
let style = window.getComputedStyle(card); // Get style of the Light DOM Card
this.shadowRoot.querySelector('.card').style = style; // Set the ShadowDOM card style equal to the Light DOM Style
console.log(style);
console.log(style.color); // yellow = rgb:255,255,0
console.log(style.background); // green = rgb:0,128,0
card.remove(); // Remove the card from the Light DOM to prevent duplication
})
}
})
</script>
Notice that the styling above doesn't apply even though it seems to be exactly as the docs specify:
"The returned object is the same CSSStyleDeclaration type as the object returned from the element's style property. However, the two objects have different purposes:
The object from getComputedStyle is read-only, and should be used to inspect the element's style — including those set by a element or an external stylesheet.
The element.style object should be used to set styles on that element, or inspect styles directly added to it from JavaScript manipulation or the global style attribute."
https://developer.mozilla.org/en-US/docs/Web/API/Window/getComputedStyle#description
From MDN Documentation:
The Window.getComputedStyle() method returns an object containing the values of all CSS properties of an element, after applying active stylesheets and resolving any basic computation those values may contain. Individual CSS property values are accessed through APIs provided by the object, or by indexing with CSS property names.
It's stated that you need to use API functions, such as getPropertyValue() to get the value of it.
Ref: https://developer.mozilla.org/en-US/docs/Web/API/Window/getComputedStyle
If you want to print all of the CSS styles from a specific element you may just iterate all the attributes like this:
function dumpCSSText(element){
var s = '';
var o = getComputedStyle(element);
for(var i = 0; i < o.length; i++){
s+=o[i] + ': ' + o.getPropertyValue(o[i])+';\n';
}
return s;
}
var e = document.querySelector('.card');
console.log(dumpCSSText(e));
.card {
color: #ff0;
font-size: 3rem;
font-weight: 600;
border: 3px solid blueviolet;
background-color: greenyellow;
}
<div class="card"></div>
property style is read-only so you can't assign anything to it;
(I stand corrected per comments; you can assign a value, but it
will override all values)
The innerHTML of Custom Elements is not parsed yet when the connectedCallback fires. So getting styles of its children with getComputedStyle is an operation on non-existing elements.
If you reflect the lightDOM contents to a <slot> in shadowDOM, there is no need to copy styles as the styling from lightDOM is reflected
<style>
.card {
color: yellow;
background: green;
}
</style>
<my-element>
<div class="card">lightDOM reflected to shadowDOM</div>
</my-element>
<script>
customElements.define("my-element", class extends HTMLElement {
constructor(){
super().attachShadow({mode:"open"}).innerHTML = `<slot></slot>`
}
connectedCallback() {
setTimeout(() => { // wait till innerHTML is parsed
let card = this.querySelector(".card"); // in lightDOM!
let style = window.getComputedStyle(card);
console.log(style.color); // yellow = rgb:255,255,0
console.log(style.background); // green = rgb:0,128,0
})
}
})
</script>
More reading:
https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/style
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/slot
::slotted CSS selector for nested children in shadowDOM slot
wait for Element Upgrade in connectedCallback: FireFox and Chromium differences
I would like to change the styling attribute values of all elements that have the class "post-feature" and contain an attribute value of "http"
So the div element will look like the following:
<div class="post-feature" style="backgroundimage:url(http://local.test.com/test_image.jpg);">
So far the http check works. But I am not able to set the attribute value.
I have the following code
var features = document.getElementsByClassName(".post-feature")
[0].getAttribute("style");
if (features.includes("http")) {
features.setAttribute("background-color", "orange");
} else {
alert('no change');
}
You can use querySelectorAll('.post-feature[style*="http"]') to find those elements.
Then simply iterate through them and i.e. set their background color with
element.style.backgroundColor = 'orange';
Now, if you want to make sure you only target elements having a background-image and http, you can use this selector:
querySelectorAll('.post-feature[style*="http"][style*="background-image"]')
Also, by adding an i (or I) just before the end bracket [style*="http"i], the value will be compared case-insensitively.
window.addEventListener('load', function() {
var elements = document.querySelectorAll('.post-feature[style*="http"]');
for (var i = 0; i < elements.length; i++) {
elements[i].style.backgroundColor = 'orange'; /* add propert value */
/* replace class
elements[i].className = 'myClass';
*/
/* add a class
elements[i].classList.add('myClass');
*/
}
/* temp log */
console.log('Found ', elements.length,' element(s)');
})
div {
height: 40px;
background-color: gray;
}
div + div {
margin-top: 10px;
}
<div class="post-feature" style="background-image:url(http://local.test.com/test_image.jpg);"></div>
<div class="post-feature"></div>
<div class="post-feature" style="background-image:url(http://local.test.com/test_image.jpg);"></div>
<div class="post-feature"></div>
Updated
To only change styling, like colors etc., you don't even need a script, you can use CSS alone
div {
height: 40px;
background-color: gray;
}
div + div {
margin-top: 10px;
}
/* for elements that contain "http" and "background-image" */
.post-feature[style*="http"i][style*="background-image"i] {
background-color: orange;
}
<div class="post-feature" style="background-image:url(http://local.test.com/test_image.jpg);"></div>
<div class="post-feature"></div>
<div class="post-feature" style="background-image:url(HTTP://local.test.com/test_image.jpg);"></div>
<div class="post-feature"></div>
As a note, and as discussed in a few comments, if to make sure it is the background-image property that also contain the http in its url(), you can adjust the selector to this, which as well can be used without any script, as a CSS rule
.post-feature[style*="background-image:url(http"i] {
background-color: orange;
}
The above selector can of course also be used in the first sample, like this
querySelectorAll('.post-feature[style*="background-image:url(http"i]')
First, you can use querySelctorAll() with a CSS query that selects the elements with the class you desire and, in most cases, you should use this instead of getElementsByClassName() as that returns a "live node list" that causes the DOM to be re-scanned every time you access it.
Next, setAttribute() is for setting HTML element attributes. You are asking to change the value of a CSS property. While that could be accomplished with setAttribute('style', value), it is very "old-school" and not the best approach, nor is getAttribute('style') the best way to read a CSS property value (it won't work if the CSS was set from a style sheet).
Also, your code is trying to access: backgroundimage, but the property is accessed as background-image when working in CSS and backgroundImage when accessing it via JavaScript.
To access the inline styles applied to an HTML element, just access the style property of that element, followed by the name of the CSS property you are interested in. For example:
var bColor = element.style.backgroundColor;
If the style has been applied to the element from an internal style sheet or an external style sheet, the above approach won't work for you and you'll need to get it another way, via window.getComputedStyle():
var bColor = window.getComputedStyle(element, null).backgroundColor;
But, note that getComputedStyle() doesn't always return the same value that you set - - it's the value after the browser has computed all factors. In this case, even paths that you wrote as relative references (without the "http") will be returned as absolute paths (with the http).
So, here is a modern approach that correctly checks only the background-image CSS property for the presence of http.
NOTE: This solution tests for http specifically in the background-image property. Unlike most of the other answers given, this code will correctly ignore http in other CSS properties besides background-image. Examine the CSS of the last div to see this in action.
// querySelectorAll() is more efficient than getElementsByClassName()
var features = document.querySelectorAll(".post-feature");
// Loop over the list
for(var i = 0; i < features.length; i++){
// Get access to the background-image property (called backgroundImage from JavaScript) value,
// convert that value to lower case and check to see if "http" is in that value
if(features[i].style.backgroundImage.toLowerCase().indexOf("http") > -1){
// Set the CSS background-color property (called "backgroundColor" in JavaScript) to orange:
features[i].style.backgroundColor = "orange";
// Just for testing:
features[i].textContent = features[i].style.backgroundImage;
} else {
alert("No change");
}
}
.post-feature { width:100%; height:50px; border:1px solid black; background-color:gray; color:yellow; }
<!-- The correct CSS property is "background-image", not "backgroundimage" -->
<div class="post-feature" style="background-image:url(http://local.test.com/test_image.jpg);"></div>
<div class="post-feature" style="background-image:url(test_image.jpg);"></div>
<div class="post-feature" style="background-image:url(http://local.test.com/test_image.jpg);"></div>
<div class="post-feature"
style="border-image: url('http:///images/border.png') 30 30 repeat;background-image:url(test_image.jpg);">I have "http" in one of my CSS properties, but not "background-image", so I shouldn't be orange.</div>
i think some wrong in your code, try this code
element.setAttribute("style", "background-color: orange;"); // bad
or
element.style.backgroundColor = "orange"; // good
Use element.style.backgroundColor and indexOf
var features = document.getElementsByClassName(".post-feature")[0].getAttribute("style");
if (features.indexOf("http") > -1) {
features.style.backgroundColor = "orange";
} else {
alert('no change');
}
check this fiddle
https://jsfiddle.net/vywk72j8/2/
<div class="post-feature" style="background-image:url(http://local.test.com/test_image.jpg);">
tt</div>
var feature = document.getElementsByClassName("post-feature")[0];
if (feature.style.backgroundImage.indexOf("http") !== -1) {
feature.style.backgroundColor = "orange";
} else {
alert('no change');
}
In your code, you are fetching the attribute value in features
var features = document.getElementsByClassName(".post-feature")
[0].getAttribute("style");
Here features is a string containing attribute value, not an element so you cannot use it to set value.
It's easy to set inline CSS values with javascript. If I want to change the width and I have html like this:
<div style="width: 10px"></div>
All I need to do is:
document.getElementById('id').style.width = value;
It will change the inline stylesheet values. Normally this isn't a problem, because the inline style overrides the stylesheet. Example:
<style>
#tId {
width: 50%;
}
</style>
<div id="tId"></div>
Using this Javascript:
document.getElementById('tId').style.width = "30%";
I get the following:
<style>
#tId {
width: 50%;
}
</style>
<div id="tId" style="width: 30%";></div>
This is a problem, because not only do I not want to change inline values, If I look for the width before I set it, when I have:
<div id="tId"></div>
The value returned is Null, so if I have Javascript that needs to know the width of something to do some logic (I increase the width by 1%, not to a specific value), getting back Null when I expect the string "50%" doesn't really work.
So my question: I have values in a CSS style that are not located inline, how can I get these values? How can I modify the style instead of the inline values, given an id?
Ok, it sounds like you want to change the global CSS so which will effictively change all elements of a peticular style at once. I've recently learned how to do this myself from a Shawn Olson tutorial. You can directly reference his code here.
Here is the summary:
You can retrieve the stylesheets via document.styleSheets. This will actually return an array of all the stylesheets in your page, but you can tell which one you are on via the document.styleSheets[styleIndex].href property. Once you have found the stylesheet you want to edit, you need to get the array of rules. This is called "rules" in IE and "cssRules" in most other browsers. The way to tell what CSSRule you are on is by the selectorText property. The working code looks something like this:
var cssRuleCode = document.all ? 'rules' : 'cssRules'; //account for IE and FF
var rule = document.styleSheets[styleIndex][cssRuleCode][ruleIndex];
var selector = rule.selectorText; //maybe '#tId'
var value = rule.value; //both selectorText and value are settable.
Let me know how this works for ya, and please comment if you see any errors.
Please! Just ask w3 (http://www.quirksmode.org/dom/w3c_css.html)!
Or actually, it took me five hours... but here it is!
function css(selector, property, value) {
for (var i=0; i<document.styleSheets.length;i++) {//Loop through all styles
//Try add rule
try { document.styleSheets[i].insertRule(selector+ ' {'+property+':'+value+'}', document.styleSheets[i].cssRules.length);
} catch(err) {try { document.styleSheets[i].addRule(selector, property+':'+value);} catch(err) {}}//IE
}
}
The function is really easy to use.. example:
<div id="box" class="boxes" onclick="css('#box', 'color', 'red')">Click Me!</div>
Or:
<div class="boxes" onmouseover="css('.boxes', 'color', 'green')">Mouseover Me!</div>
Or:
<div class="boxes" onclick="css('body', 'border', '1px solid #3cc')">Click Me!</div>
Oh..
EDIT: as #user21820 described in its answer, it might be a bit unnecessary to change all stylesheets on the page. The following script works with IE5.5 as well as latest Google Chrome, and adds only the above described css() function.
(function (scope) {
// Create a new stylesheet in the bottom
// of <head>, where the css rules will go
var style = document.createElement('style');
document.head.appendChild(style);
var stylesheet = style.sheet;
scope.css = function (selector, property, value) {
// Append the rule (Major browsers)
try { stylesheet.insertRule(selector+' {'+property+':'+value+'}', stylesheet.cssRules.length);
} catch(err) {try { stylesheet.addRule(selector, property+':'+value); // (pre IE9)
} catch(err) {console.log("Couldn't add style");}} // (alien browsers)
}
})(window);
Gathering the code in the answers, I wrote this function that seems running well on my FF 25.
function CCSStylesheetRuleStyle(stylesheet, selectorText, style, value){
/* returns the value of the element style of the rule in the stylesheet
* If no value is given, reads the value
* If value is given, the value is changed and returned
* If '' (empty string) is given, erases the value.
* The browser will apply the default one
*
* string stylesheet: part of the .css name to be recognized, e.g. 'default'
* string selectorText: css selector, e.g. '#myId', '.myClass', 'thead td'
* string style: camelCase element style, e.g. 'fontSize'
* string value optionnal : the new value
*/
var CCSstyle = undefined, rules;
for(var m in document.styleSheets){
if(document.styleSheets[m].href.indexOf(stylesheet) != -1){
rules = document.styleSheets[m][document.all ? 'rules' : 'cssRules'];
for(var n in rules){
if(rules[n].selectorText == selectorText){
CCSstyle = rules[n].style;
break;
}
}
break;
}
}
if(value == undefined)
return CCSstyle[style]
else
return CCSstyle[style] = value
}
This is a way to put values in the css that will be used in JS even if not understood by the browser. e.g. maxHeight for a tbody in a scrolled table.
Call :
CCSStylesheetRuleStyle('default', "#mydiv", "height");
CCSStylesheetRuleStyle('default', "#mydiv", "color", "#EEE");
I don't know why the other solutions go through the whole list of stylesheets for the document. Doing so creates a new entry in each stylesheet, which is inefficient. Instead, we can simply append a new stylesheet and simply add our desired CSS rules there.
style=document.createElement('style');
document.head.appendChild(style);
stylesheet=style.sheet;
function css(selector,property,value)
{
try{ stylesheet.insertRule(selector+' {'+property+':'+value+'}',stylesheet.cssRules.length); }
catch(err){}
}
Note that we can override even inline styles set directly on elements by adding " !important" to the value of the property, unless there already exist more specific "!important" style declarations for that property.
I don't have rep enough to comment so I'll format an answer, yet it is only a demonstration of the issue in question.
It seems, when element styles are defined in stylesheets they are not visible to getElementById("someElement").style
This code illustrates the issue... Code from below on jsFiddle.
In Test 2, on the first call, the items left value is undefined, and so, what should be a simple toggle gets messed up. For my use I will define my important style values inline, but it does seem to partially defeat the purpose of the stylesheet.
Here's the page code...
<html>
<head>
<style type="text/css">
#test2a{
position: absolute;
left: 0px;
width: 50px;
height: 50px;
background-color: green;
border: 4px solid black;
}
#test2b{
position: absolute;
left: 55px;
width: 50px;
height: 50px;
background-color: yellow;
margin: 4px;
}
</style>
</head>
<body>
<!-- test1 -->
Swap left positions function with styles defined inline.
Test 1<br>
<div class="container">
<div id="test1a" style="position: absolute;left: 0px;width: 50px; height: 50px;background-color: green;border: 4px solid black;"></div>
<div id="test1b" style="position: absolute;left: 55px;width: 50px; height: 50px;background-color: yellow;margin: 4px;"></div>
</div>
<script type="text/javascript">
function test1(){
var a = document.getElementById("test1a");
var b = document.getElementById("test1b");
alert(a.style.left + " - " + b.style.left);
a.style.left = (a.style.left == "0px")? "55px" : "0px";
b.style.left = (b.style.left == "0px")? "55px" : "0px";
}
</script>
<!-- end test 1 -->
<!-- test2 -->
<div id="moveDownThePage" style="position: relative;top: 70px;">
Identical function with styles defined in stylesheet.
Test 2<br>
<div class="container">
<div id="test2a"></div>
<div id="test2b"></div>
</div>
</div>
<script type="text/javascript">
function test2(){
var a = document.getElementById("test2a");
var b = document.getElementById("test2b");
alert(a.style.left + " - " + b.style.left);
a.style.left = (a.style.left == "0px")? "55px" : "0px";
b.style.left = (b.style.left == "0px")? "55px" : "0px";
}
</script>
<!-- end test 2 -->
</body>
</html>
I hope this helps to illuminate the issue.
Skip
You can get the "computed" styles of any element.
IE uses something called "currentStyle", Firefox (and I assume other "standard compliant" browsers) uses "defaultView.getComputedStyle".
You'll need to write a cross browser function to do this, or use a good Javascript framework like prototype or jQuery (search for "getStyle" in the prototype javascript file, and "curCss" in the jquery javascript file).
That said if you need the height or width you should probably use element.offsetHeight and element.offsetWidth.
The value returned is Null, so if I have Javascript that needs to know the width of something to do some logic (I increase the width by 1%, not to a specific value)
Mind, if you add an inline style to the element in question, it can act as the "default" value and will be readable by Javascript on page load, since it is the element's inline style property:
<div style="width:50%">....</div>
This simple 32 lines gist lets you identify a given stylesheet and change its styles very easily:
var styleSheet = StyleChanger("my_custom_identifier");
styleSheet.change("darkolivegreen", "blue");
I've never seen any practical use of this, but you should probably consider DOM stylesheets. However, I honestly think that's overkill.
If you simply want to get the width and height of an element, irrespective of where the dimensions are being applied from, just use element.offsetWidth and element.offsetHeight.
Perhaps try this:
function CCSStylesheetRuleStyle(stylesheet, selectorText, style, value){
var CCSstyle = undefined, rules;
for(var m in document.styleSheets){
if(document.styleSheets[m].href.indexOf(stylesheet) != -1){
rules = document.styleSheets[m][document.all ? 'rules' : 'cssRules'];
for(var n in rules){
if(rules[n].selectorText == selectorText){
CCSstyle = rules[n].style;
break;
}
}
break;
}
}
if(value == undefined)
return CCSstyle[style]
else
return CCSstyle[style] = value
}
How would one return a class computed CSS property/property array?
Like, if I have a class defined in CSS:
.global {
background-color: red;
color: white;
text-shadow: 0px 1px 1px black;
}
It's applied on the go with javascript to an element. Now I want to change this elements childrens' color to parents' (.global) element background-color.
And is there a way to read CSS properties from a previously defined class in a style tag or externally included *.css?
Something like, getCSSData([span|.global|div > h1]); (where the passed variable is a CSS selector, that gets data for exactly matching element) that would return an object with each property in it's own accessible variable?
Something like:
cssdata = {
selector : '.global',
properties : {
backgroundColor : 'red',
color : 'white',
textShadow : '0px 1px 1px black'
// plus inherited, default ones (the ones specified by W3..)
}
}
And the usage for my previously explained example would be:
// just an example to include both, jQuery usage and/or native javascript
var elements = $('.global').children() || document.getElementsByClassName('.global')[0].children;
var data = $('.global').getCSSData() || document.getCSSData('.global');
return elements.css('color', data.properties.backgroundColor) || elements.style.backgroundColor = data.properties.backgroundColor;
Is there a function built in already in javascript/jquery and I've overlooked it?
If not, what should I look for to make one?
P.S. Can be DOM Level 3 too.. (HTML5'ish..)
If you want to grab the background color of the parent element and then apply that color to the font of all of it's children you could use the following code.
$(document).ready(function(){
var global = $('.global');
var bgColor = global.css('background-color');
global.children().css('color', bgColor);
};
Here's an example on jsFiddle.net
You can access the computedStyle of an element which includes all inherited style values, here is a example that outputs the computed style of a div element in the console.
<script type="text/javascript">
if (document.addEventListener) {
document.addEventListener("DOMContentLoaded", listComputedStyles, false);
}
function listComputedStyles() {
var element = document.getElementById("myDiv");
var properties = window.getComputedStyle(element, null);
for (var i = 0; i < properties.length; i++)
{
var value = window.getComputedStyle(element, null).getPropertyValue(properties[i]);
console.log(properties[i], value);
}
}
</script>
<div id="myDiv" style="background-color: blue; height: 500px;"></div>
You can find more information here: http://help.dottoro.com/ljscsoax.php
If I understand your question correctly, you'd like to find a general approach to modifying a class; and to have that modifcation affect all of the instantiations of that class. This was the subject of another detailed discussion on SO over here.
There turned out to be an extremely interesting and useful treatment of classes that works in almost all browsers, notably excepting IE8 and below.
It's easy to set inline CSS values with javascript. If I want to change the width and I have html like this:
<div style="width: 10px"></div>
All I need to do is:
document.getElementById('id').style.width = value;
It will change the inline stylesheet values. Normally this isn't a problem, because the inline style overrides the stylesheet. Example:
<style>
#tId {
width: 50%;
}
</style>
<div id="tId"></div>
Using this Javascript:
document.getElementById('tId').style.width = "30%";
I get the following:
<style>
#tId {
width: 50%;
}
</style>
<div id="tId" style="width: 30%";></div>
This is a problem, because not only do I not want to change inline values, If I look for the width before I set it, when I have:
<div id="tId"></div>
The value returned is Null, so if I have Javascript that needs to know the width of something to do some logic (I increase the width by 1%, not to a specific value), getting back Null when I expect the string "50%" doesn't really work.
So my question: I have values in a CSS style that are not located inline, how can I get these values? How can I modify the style instead of the inline values, given an id?
Ok, it sounds like you want to change the global CSS so which will effictively change all elements of a peticular style at once. I've recently learned how to do this myself from a Shawn Olson tutorial. You can directly reference his code here.
Here is the summary:
You can retrieve the stylesheets via document.styleSheets. This will actually return an array of all the stylesheets in your page, but you can tell which one you are on via the document.styleSheets[styleIndex].href property. Once you have found the stylesheet you want to edit, you need to get the array of rules. This is called "rules" in IE and "cssRules" in most other browsers. The way to tell what CSSRule you are on is by the selectorText property. The working code looks something like this:
var cssRuleCode = document.all ? 'rules' : 'cssRules'; //account for IE and FF
var rule = document.styleSheets[styleIndex][cssRuleCode][ruleIndex];
var selector = rule.selectorText; //maybe '#tId'
var value = rule.value; //both selectorText and value are settable.
Let me know how this works for ya, and please comment if you see any errors.
Please! Just ask w3 (http://www.quirksmode.org/dom/w3c_css.html)!
Or actually, it took me five hours... but here it is!
function css(selector, property, value) {
for (var i=0; i<document.styleSheets.length;i++) {//Loop through all styles
//Try add rule
try { document.styleSheets[i].insertRule(selector+ ' {'+property+':'+value+'}', document.styleSheets[i].cssRules.length);
} catch(err) {try { document.styleSheets[i].addRule(selector, property+':'+value);} catch(err) {}}//IE
}
}
The function is really easy to use.. example:
<div id="box" class="boxes" onclick="css('#box', 'color', 'red')">Click Me!</div>
Or:
<div class="boxes" onmouseover="css('.boxes', 'color', 'green')">Mouseover Me!</div>
Or:
<div class="boxes" onclick="css('body', 'border', '1px solid #3cc')">Click Me!</div>
Oh..
EDIT: as #user21820 described in its answer, it might be a bit unnecessary to change all stylesheets on the page. The following script works with IE5.5 as well as latest Google Chrome, and adds only the above described css() function.
(function (scope) {
// Create a new stylesheet in the bottom
// of <head>, where the css rules will go
var style = document.createElement('style');
document.head.appendChild(style);
var stylesheet = style.sheet;
scope.css = function (selector, property, value) {
// Append the rule (Major browsers)
try { stylesheet.insertRule(selector+' {'+property+':'+value+'}', stylesheet.cssRules.length);
} catch(err) {try { stylesheet.addRule(selector, property+':'+value); // (pre IE9)
} catch(err) {console.log("Couldn't add style");}} // (alien browsers)
}
})(window);
Gathering the code in the answers, I wrote this function that seems running well on my FF 25.
function CCSStylesheetRuleStyle(stylesheet, selectorText, style, value){
/* returns the value of the element style of the rule in the stylesheet
* If no value is given, reads the value
* If value is given, the value is changed and returned
* If '' (empty string) is given, erases the value.
* The browser will apply the default one
*
* string stylesheet: part of the .css name to be recognized, e.g. 'default'
* string selectorText: css selector, e.g. '#myId', '.myClass', 'thead td'
* string style: camelCase element style, e.g. 'fontSize'
* string value optionnal : the new value
*/
var CCSstyle = undefined, rules;
for(var m in document.styleSheets){
if(document.styleSheets[m].href.indexOf(stylesheet) != -1){
rules = document.styleSheets[m][document.all ? 'rules' : 'cssRules'];
for(var n in rules){
if(rules[n].selectorText == selectorText){
CCSstyle = rules[n].style;
break;
}
}
break;
}
}
if(value == undefined)
return CCSstyle[style]
else
return CCSstyle[style] = value
}
This is a way to put values in the css that will be used in JS even if not understood by the browser. e.g. maxHeight for a tbody in a scrolled table.
Call :
CCSStylesheetRuleStyle('default', "#mydiv", "height");
CCSStylesheetRuleStyle('default', "#mydiv", "color", "#EEE");
I don't know why the other solutions go through the whole list of stylesheets for the document. Doing so creates a new entry in each stylesheet, which is inefficient. Instead, we can simply append a new stylesheet and simply add our desired CSS rules there.
style=document.createElement('style');
document.head.appendChild(style);
stylesheet=style.sheet;
function css(selector,property,value)
{
try{ stylesheet.insertRule(selector+' {'+property+':'+value+'}',stylesheet.cssRules.length); }
catch(err){}
}
Note that we can override even inline styles set directly on elements by adding " !important" to the value of the property, unless there already exist more specific "!important" style declarations for that property.
I don't have rep enough to comment so I'll format an answer, yet it is only a demonstration of the issue in question.
It seems, when element styles are defined in stylesheets they are not visible to getElementById("someElement").style
This code illustrates the issue... Code from below on jsFiddle.
In Test 2, on the first call, the items left value is undefined, and so, what should be a simple toggle gets messed up. For my use I will define my important style values inline, but it does seem to partially defeat the purpose of the stylesheet.
Here's the page code...
<html>
<head>
<style type="text/css">
#test2a{
position: absolute;
left: 0px;
width: 50px;
height: 50px;
background-color: green;
border: 4px solid black;
}
#test2b{
position: absolute;
left: 55px;
width: 50px;
height: 50px;
background-color: yellow;
margin: 4px;
}
</style>
</head>
<body>
<!-- test1 -->
Swap left positions function with styles defined inline.
Test 1<br>
<div class="container">
<div id="test1a" style="position: absolute;left: 0px;width: 50px; height: 50px;background-color: green;border: 4px solid black;"></div>
<div id="test1b" style="position: absolute;left: 55px;width: 50px; height: 50px;background-color: yellow;margin: 4px;"></div>
</div>
<script type="text/javascript">
function test1(){
var a = document.getElementById("test1a");
var b = document.getElementById("test1b");
alert(a.style.left + " - " + b.style.left);
a.style.left = (a.style.left == "0px")? "55px" : "0px";
b.style.left = (b.style.left == "0px")? "55px" : "0px";
}
</script>
<!-- end test 1 -->
<!-- test2 -->
<div id="moveDownThePage" style="position: relative;top: 70px;">
Identical function with styles defined in stylesheet.
Test 2<br>
<div class="container">
<div id="test2a"></div>
<div id="test2b"></div>
</div>
</div>
<script type="text/javascript">
function test2(){
var a = document.getElementById("test2a");
var b = document.getElementById("test2b");
alert(a.style.left + " - " + b.style.left);
a.style.left = (a.style.left == "0px")? "55px" : "0px";
b.style.left = (b.style.left == "0px")? "55px" : "0px";
}
</script>
<!-- end test 2 -->
</body>
</html>
I hope this helps to illuminate the issue.
Skip
You can get the "computed" styles of any element.
IE uses something called "currentStyle", Firefox (and I assume other "standard compliant" browsers) uses "defaultView.getComputedStyle".
You'll need to write a cross browser function to do this, or use a good Javascript framework like prototype or jQuery (search for "getStyle" in the prototype javascript file, and "curCss" in the jquery javascript file).
That said if you need the height or width you should probably use element.offsetHeight and element.offsetWidth.
The value returned is Null, so if I have Javascript that needs to know the width of something to do some logic (I increase the width by 1%, not to a specific value)
Mind, if you add an inline style to the element in question, it can act as the "default" value and will be readable by Javascript on page load, since it is the element's inline style property:
<div style="width:50%">....</div>
This simple 32 lines gist lets you identify a given stylesheet and change its styles very easily:
var styleSheet = StyleChanger("my_custom_identifier");
styleSheet.change("darkolivegreen", "blue");
I've never seen any practical use of this, but you should probably consider DOM stylesheets. However, I honestly think that's overkill.
If you simply want to get the width and height of an element, irrespective of where the dimensions are being applied from, just use element.offsetWidth and element.offsetHeight.
Perhaps try this:
function CCSStylesheetRuleStyle(stylesheet, selectorText, style, value){
var CCSstyle = undefined, rules;
for(var m in document.styleSheets){
if(document.styleSheets[m].href.indexOf(stylesheet) != -1){
rules = document.styleSheets[m][document.all ? 'rules' : 'cssRules'];
for(var n in rules){
if(rules[n].selectorText == selectorText){
CCSstyle = rules[n].style;
break;
}
}
break;
}
}
if(value == undefined)
return CCSstyle[style]
else
return CCSstyle[style] = value
}