How to get computed style and the source of this rule? [duplicate] - javascript

This question already has answers here:
Find all CSS rules that apply to an element
(10 answers)
Closed 5 years ago.
I want to get the element computed style and the css (file and line) that applies that rule. Similar to what Chrome Dev Tools does when the "Computed" tab is used and you click on that arrow beside the value.
In short, I want to be able to, using javascript, find out these two things:
What is the CSS value that is actually being applied to that element (computed style)
Once I found the computed style, I want to know where it comes from (like file name and line number)
I know this can be done manually using devtools, but I need this done by a script.
Thanks

You can use Window.getComputedStyle(). An example of usage:
<style>
#elem-container{
position: absolute;
left: 100px;
top: 200px;
height: 100px;
}
</style>
<div id="elem-container">dummy</div>
<div id="output"></div>
<script>
function getTheStyle(){
var elem = document.getElementById("elem-container");
var theCSSprop = window.getComputedStyle(elem,null).getPropertyValue("height");
document.getElementById("output").innerHTML = theCSSprop;
}
getTheStyle();
</script>
See MDN Documentation to learn more how to use this feature and it's compatibility with different browsers.
Unfortunately, this approach will not give you the location of where this value comes from.

Related

Set Property Value of Pseudo-Elements Using JavaScript [duplicate]

This question already has answers here:
Selecting and manipulating CSS pseudo-elements such as ::before and ::after using javascript (or jQuery)
(26 answers)
How to update placeholder color using Javascript?
(5 answers)
Closed 2 years ago.
Is it possible to change a CSS pseudo-element style via JavaScript?
For example, I want to dynamically set the color of the scrollbar like so:
document.querySelector("#editor::-webkit-scrollbar-thumb:vertical").style.background = localStorage.getItem("Color");
and I also want to be able to tell the scrollbar to hide like so:
document.querySelector("#editor::-webkit-scrollbar").style.visibility = "hidden";
Both of these scripts, however, return:
Uncaught TypeError: Cannot read property 'style' of null
Is there some other way of going about this?
Cross-browser interoperability is not important, I just need it to work in webkit browsers.
If you're comfortable with some graceful degradation in older browsers you can use CSS Vars. Definitely the easiest of the methods I've seen here and elsewhere.
So in your CSS you can write:
#editor {
--scrollbar-background: #ccc;
}
#editor::-webkit-scrollbar-thumb:vertical {
/* Fallback */
background-color: #ccc;
/* Dynamic value */
background-color: var(--scrollbar-background);
}
Then in your JS you can manipulate that value on the #editor element:
document.getElementById("#editor").style.setProperty('--scrollbar-background', localStorage.getItem("Color"));
Lots of other examples of manipulating CSS vars with JS here: https://eager.io/blog/communicating-between-javascript-and-css-with-css-variables/
To edit an existing one which you don't have a direct reference to requires iterating all style sheets on the page and then iterating all rules in each and then string matching the selector.
Here's a reference to a method I posted for adding new CSS for pseudo-elements, the easy version where you're setting from js
Javascript set CSS :after styles
var addRule = (function (style) {
var sheet = document.head.appendChild(style).sheet;
return function (selector, css) {
var propText = typeof css === "string" ? css : Object.keys(css).map(function (p) {
return p + ":" + (p === "content" ? "'" + css[p] + "'" : css[p]);
}).join(";");
sheet.insertRule(selector + "{" + propText + "}", sheet.cssRules.length);
};
})(document.createElement("style"));
addRule("p:before", {
display: "block",
width: "100px",
height: "100px",
background: "red",
"border-radius": "50%",
content: "''"
});
sheet.insertRule returns the index of the new rule which you can use to get a reference to it for it which can be used later to edit it.
EDIT: There is technically a way of directly changing CSS pseudo-element styles via JavaScript, as this answer describes, but the method provided here is preferable.
The closest to changing the style of a pseudo-element in JavaScript is adding and removing classes, then using the pseudo-element with those classes. An example to hide the scrollbar:
CSS
.hidden-scrollbar::-webkit-scrollbar {
visibility: hidden;
}
JavaScript
document.getElementById("editor").classList.add('hidden-scrollbar');
To later remove the same class, you could use:
document.getElementById("editor").classList.remove('hidden-scrollbar');
I changed the background of the ::selection pseudo-element by using CSS custom properties doing the following:
/*CSS Part*/
:root {
--selection-background: #000000;
}
#editor::selection {
background: var(--selection-background);
}
//JavaScript Part
document.documentElement.style.setProperty("--selection-background", "#A4CDFF");
You can't apply styles to psuedo-elements in JavaScript.
You can, however, append a <style> tag to the head of your document (or have a placeholding <style id='mystyles'> and change its content), which adjusts the styles. (This would work better than loading in another stylesheet, because embedded <style> tags have higher precedence than <link>'d ones, making sure you don't get cascading problems.
Alternatively, you could use different class names and have them defined with different psuedo-element styles in the original stylesheet.
I posted a question similar to, but not completely like, this question.
I found a way to retrieve and change styles for pseudo elements and asked what people thought of the method.
My question is at Retrieving or changing css rules for pseudo elements
Basically, you can get a style via a statement such as:
document.styleSheets[0].cssRules[0].style.backgroundColor
And change one with:
document.styleSheets[0].cssRules[0].style.backgroundColor = newColor;
You, of course, have to change the stylesheet and cssRules index. Read my question and the comments it drew.
I've found this works for pseudo elements as well as "regular" element/styles.
An old question, but one I came across when try to dynamically change the colour of the content of an element's :before selector.
The simplest solution I can think of is to use CSS variables, a solution not applicable when the question was asked:
"#editor::-webkit-scrollbar-thumb:vertical {
background: --editorScrollbarClr
}
Change the value in JavaScript:
document.body.style.setProperty(
'--editorScrollbarClr',
localStorage.getItem("Color")
);
The same can be done for other properties.
Looks like querySelector won't work with pseudo-classes/pseudo-elements, at least not those. The only thing I can think of is to dynamically add a stylesheet (or change an existing one) to do what you need.
Lots of good examples here:
How do I load css rules dynamically in Webkit (Safari/Chrome)?

Using JS, how can I detect adblockers? [duplicate]

This question already has answers here:
How to detect Adblock on my website?
(46 answers)
Closed 3 years ago.
With some simple javascript, how can I detect if the client user is using an Adblocker?
Adblockers detect scripts called ads.js or scripts with similar names and then block them so that they don't run. They also detect id's and classes that have suspicious names and simply remove them from the DOM. So here is one simple trick (explanation below) that can help you detect if your user is using an adblocker or not:
<div id="randomDiv">
<div class="adBanner">
</div>
</div>
This HTML simply places a random div on your page with only one child, an empty div that has a class of adBanner. Now an adblocker would think of the child div as an advertisement, and it would remove it.
Using CSS, we can give the .adBanner class a fixed height and a fixed width, so that it renders something on the screen.
.adBanner {
height: 2px;
width: 2px;
visibility: hidden;
}
This CSS simply gives our fake "adBanner" element a fixed width and height that we can check for later, and hides it from the user.
Now using jQuery, we can check for the height or the width of the element. We do this because if the adblocker were to remove this element from the DOM, then the height would not exist.
if ($("#randomDiv").height() > 1) {
console.log("No Adblocker!!");
}
else {
console.log("An adblocker was detected!!");
}
I'm sure there are other ways to do this, but this is just one of the ways.
Hope this helps!!!

Change html Text with conditional css but without js

Sorry about this absolutely newbie question, but I've been searching for an already similar post, and couldn't find it.
My question is:
I have a paragraph text in my HTML code which I want to automatically change into a new text once I click a specific Button.
Can this be done with CSS only, without any javascript?
Since some users block javascript, that's why I was looking for a way around...
Thanks a lot.
actually #Vaidya & #Preet it is possible via css only :
https://css-tricks.com/swapping-out-text-five-different-ways/
#fana you'll need to use a plus selector or tilde selector to make the changes affect the following div not itself but other than that you're good to go.
I can see that using css to replace content is strongly discouraged within the stackoverflow community. However I haven't found another cause other then that of code cleanliness.
I really think in coming years the true potential of CSS/SASS will unravel and people will cease to see the programmatic/dynamic as strictly excluded from CSS/SASS.
It can't be done through CSS You must need to add a script for an on-click event.
I know it is not what you exactly want but it can give you idea about it and with some changes you can make it.(but conditional and on click event using css is definitely not possible, you need javascript for that)
If you can make it work on Text click itself then it is easily possible. You only need a checkbox which is hidden and label in which you will show text. On click of text you can swap into anther text with only css:
#example {
position: relative;
}
#example-checkbox {
display: none;
}
#example-checkbox:checked + #example:after {
content: "Hide";
position: absolute;
top: 0;
left: 0;
right: 0;
bottom: 0;
background: white;
}
<input id="example-checkbox" type="checkbox">
<label for="example-checkbox" id="example">Show</label>
Reference See css only part.
Hope it will help you.

access a set of seclectors with :before using javascript [duplicate]

This question already has answers here:
Selecting and manipulating CSS pseudo-elements such as ::before and ::after using javascript (or jQuery)
(26 answers)
How to update placeholder color using Javascript?
(5 answers)
Closed 2 years ago.
Is it possible to change a CSS pseudo-element style via JavaScript?
For example, I want to dynamically set the color of the scrollbar like so:
document.querySelector("#editor::-webkit-scrollbar-thumb:vertical").style.background = localStorage.getItem("Color");
and I also want to be able to tell the scrollbar to hide like so:
document.querySelector("#editor::-webkit-scrollbar").style.visibility = "hidden";
Both of these scripts, however, return:
Uncaught TypeError: Cannot read property 'style' of null
Is there some other way of going about this?
Cross-browser interoperability is not important, I just need it to work in webkit browsers.
If you're comfortable with some graceful degradation in older browsers you can use CSS Vars. Definitely the easiest of the methods I've seen here and elsewhere.
So in your CSS you can write:
#editor {
--scrollbar-background: #ccc;
}
#editor::-webkit-scrollbar-thumb:vertical {
/* Fallback */
background-color: #ccc;
/* Dynamic value */
background-color: var(--scrollbar-background);
}
Then in your JS you can manipulate that value on the #editor element:
document.getElementById("#editor").style.setProperty('--scrollbar-background', localStorage.getItem("Color"));
Lots of other examples of manipulating CSS vars with JS here: https://eager.io/blog/communicating-between-javascript-and-css-with-css-variables/
To edit an existing one which you don't have a direct reference to requires iterating all style sheets on the page and then iterating all rules in each and then string matching the selector.
Here's a reference to a method I posted for adding new CSS for pseudo-elements, the easy version where you're setting from js
Javascript set CSS :after styles
var addRule = (function (style) {
var sheet = document.head.appendChild(style).sheet;
return function (selector, css) {
var propText = typeof css === "string" ? css : Object.keys(css).map(function (p) {
return p + ":" + (p === "content" ? "'" + css[p] + "'" : css[p]);
}).join(";");
sheet.insertRule(selector + "{" + propText + "}", sheet.cssRules.length);
};
})(document.createElement("style"));
addRule("p:before", {
display: "block",
width: "100px",
height: "100px",
background: "red",
"border-radius": "50%",
content: "''"
});
sheet.insertRule returns the index of the new rule which you can use to get a reference to it for it which can be used later to edit it.
EDIT: There is technically a way of directly changing CSS pseudo-element styles via JavaScript, as this answer describes, but the method provided here is preferable.
The closest to changing the style of a pseudo-element in JavaScript is adding and removing classes, then using the pseudo-element with those classes. An example to hide the scrollbar:
CSS
.hidden-scrollbar::-webkit-scrollbar {
visibility: hidden;
}
JavaScript
document.getElementById("editor").classList.add('hidden-scrollbar');
To later remove the same class, you could use:
document.getElementById("editor").classList.remove('hidden-scrollbar');
I changed the background of the ::selection pseudo-element by using CSS custom properties doing the following:
/*CSS Part*/
:root {
--selection-background: #000000;
}
#editor::selection {
background: var(--selection-background);
}
//JavaScript Part
document.documentElement.style.setProperty("--selection-background", "#A4CDFF");
You can't apply styles to psuedo-elements in JavaScript.
You can, however, append a <style> tag to the head of your document (or have a placeholding <style id='mystyles'> and change its content), which adjusts the styles. (This would work better than loading in another stylesheet, because embedded <style> tags have higher precedence than <link>'d ones, making sure you don't get cascading problems.
Alternatively, you could use different class names and have them defined with different psuedo-element styles in the original stylesheet.
I posted a question similar to, but not completely like, this question.
I found a way to retrieve and change styles for pseudo elements and asked what people thought of the method.
My question is at Retrieving or changing css rules for pseudo elements
Basically, you can get a style via a statement such as:
document.styleSheets[0].cssRules[0].style.backgroundColor
And change one with:
document.styleSheets[0].cssRules[0].style.backgroundColor = newColor;
You, of course, have to change the stylesheet and cssRules index. Read my question and the comments it drew.
I've found this works for pseudo elements as well as "regular" element/styles.
An old question, but one I came across when try to dynamically change the colour of the content of an element's :before selector.
The simplest solution I can think of is to use CSS variables, a solution not applicable when the question was asked:
"#editor::-webkit-scrollbar-thumb:vertical {
background: --editorScrollbarClr
}
Change the value in JavaScript:
document.body.style.setProperty(
'--editorScrollbarClr',
localStorage.getItem("Color")
);
The same can be done for other properties.
Looks like querySelector won't work with pseudo-classes/pseudo-elements, at least not those. The only thing I can think of is to dynamically add a stylesheet (or change an existing one) to do what you need.
Lots of good examples here:
How do I load css rules dynamically in Webkit (Safari/Chrome)?

can i give a name to the css property [duplicate]

This question already has answers here:
Creating CSS Global Variables : Stylesheet theme management [duplicate]
(6 answers)
Is there any way to use variables in css?
(3 answers)
Closed 8 years ago.
Here is an example:
This is the normal css:
h1{
background-color: #fafafa;
}
I would like to change this to the following:
h1{
background-color: default or any id name
}
Where can I give a javascript command to change this color code(i.e #fafafa)? Where ever it is in the stylesheet to default or any id name.
So that I can use it in a color switcher to change the color for this code. I don't want to use less because I have already gone way to far in my project.
You can not do that as CSS is completely static what you can do is when you want to change the color for that element on a particular condition you can add an id to the element using javascript/jQuery by enclosing the element in a span/div in the first place. and write a new css for that particular id. so on your desired event new css will apply to that element and color will be changed at runtime.
Either you use some variables for example in the style you can use this:
var width = "150px";
And in the container use something like:
<div style="width: #width">A div with width 150px.</div>
But brother there is no default value for them.
As the code you are showing is using a hex value for a color. That cannot be converted to a default name. However using variable can do it. Or you can try using rgba. But there isn't any default name. However You can try to write the color name itself as:
color: white;
or
color: red;
But I am not sure it will work for you for your job.
You can give name to css property through this font-family
p
{
font-family:"Times New Roman",Georgia,Serif;
}

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