Develop Reference

script that applies a style to newly created elements

I am writing a tampermonkey script that changes the style of an element whose class starts with "blocked". So i have this code:
var blockedelements = document.querySelectorAll("[class^=blocked]");
var element = blockedelements[0];
element.style.display="none";
for simplicity this is only for the first element but i know how to iterate through each one and this code as it is works. the webapp dynamically creates new elements with this class and i want the script to execute for each newly created element which is what i don't know how to do. I want a pure JS solution, not jquery. Is this what a listener is for? i don't know much about javascript.
I would appreciate any pointers, thanks

Instead of manually changing the display value for every instance of the element, you could use JavaScript to add a page-wide style rule to hide all of them. That way you can let the browser handle applying the rule to both existing and future instances of the element for you.
Rough idea:
var rule = "[class^=blocked] { display: none }";
var styleElement = document.createElement("style");
styleElement.type = "text/css";
if (styleElement.style.cssText) {
styleElement.style.cssText = rule;
} else {
styleElement.appendChild(document.createTextNode(rule));
}
document.getElementsByTagName("head")[0].appendChild(styleElement);

The margins in div of new tab not at all taking effect

Hi I am creating dynamic form in new tab using JavaScript. Margin effects on div are not taking effect. I am neither able to set the margins using class and id in css nor using div.setAttribute. Below is the code.
`
var openWindow = window.open('dynForm.html','_blank','');
var windoc=openWindow.document;
windoc.write("This is dynamic form ");
var div=document.createElement("div");
div.setAttribute("style","border:solid");
div.setAttribute("style","margin-left:1cm");
div.setAttribute("style","margin-right:1cm");
div.setAttribute("style","margin-bottom:1cm");
div.setAttribute("style","margin-top:1cm");
div.setAttribute("style","background-color:lightblue");
`Only background color is taking effect on the new tab. The below screen shot shows how the screen looks irrespective of the values of margin.
Quesstion 2: No class or id attribute in my css is being applied to div.
#myDIV2{
background-color:lightblue;
}
I tried div.id="myDIV2";
I also tried div.setAttribute("id","myDIV2");` I applied the same using class also, but still couldn't find any difference. I do not know why its not working and what went wrong here. Please help

You're overriding the styles every time you call setAttribute, try combining the styles and then set the style attribute only once:
var openWindow = window.open('dynForm.html','_blank','');
var styles= [
"border:solid;",
"margin: 1cm;",
"background-color:lightblue;"
];
var windoc=openWindow.document;
windoc.write("This is dynamic form ");
var end_styles = "";
for (var i=0; i<styles.length;i++) {
end_styles += styles[i];
}
var div=document.createElement("div");
div.setAttribute("style", end_styles);
Note: the fiddle won't work on stackoverflow, I used it because it's easier to format code

This is happening because your all style attribute are getting overridden by previous div.setAttribute and your last attribute div.setAttribute("style","background-color:lightblue"); getting applied. Try to put all styles in one go. div.setAttribute("style","style1:value1;style2:value2;style3:value3;");

Is it possible to calculate (compute) resulting css style manually?

Is it possible to compute resulting css style on the element manually (without need to render it)?
Lets say I'm supposed to have an HTML structure:
<p style="some_style1">
<span style="some_style2">
<span style="some_style3">
TEXT
</span>
</span>
</p>
I know what are some_style1, some_style2, some_style3 in terms of JS object (for example i have data for each element like: {font: 'Times New Roman' 12px bold; text-align: center;})
I want to MANUALLY (without need to render in browser the whole structure) compute resulting style that will effect "TEXT".
What algorithm (or solution) should I use?

There exist browsers that don't need rendering in a window (headless browser). You can load a page and query what you want. It won't be easier than in a normal browser to obtain what you ask though.
JSCSSP is a CSS parser written in cross-browser JavaScript that could be a first step to achieve what you want from scratch or quite. Give it a stylesheet and it'll tell you what a browser would've parsed. You still must manage:
the DOM,
inheritance of styles,
determine which rules apply to a given element with or without class, id, attributes, siblings, etc
priorities of selectors
etc
Its author is D. Glazman, co-chairman of the W3C CSS group and developer of Kompozer, NVu and BlueGriffon so it should parse CSS as expected :)

The simplest thing I can think of is to wrap the whole thing in a a container that you set display: none on, and append it to the DOM. The browser won't render it, but you'll then be able to query the computed style.
Here's an example showing how jQuery can't find the style information when the structure isn't connected to the DOM, but when it is, it can:
jQuery(function($) {
// Disconnected structure
var x = $("<p style='color: red'><span style='padding: 2em'><span style='background-color: white'>TEXT</span></span></p>");
// Get the span
var y = x.find("span span");
// Show its computed color; will be blank
display("y.css('color'): " + y.css('color'));
// Create a hidden div and append the structure
var d = $("<div>");
d.hide();
d.append(x);
d.appendTo(document.body);
// Show the computed color now; show red
display("y.css('color'): " + y.css('color'));
// Detach it again
d.detach();
function display(msg) {
$("<p>").html(String(msg)).appendTo(document.body);
}
});
Live copy | source
I can't guarantee all values will be exactly right, you'll have to try it and see; browsers may defer calculating some things until/unless the container is visible. If you find that some properties you want aren't calculated yet, you may have to make the div visible, but off-page (position: absolute; left: -10000px);

I found some articles about this: Can jQuery get all styles applied to an element on Stackoverflow.
Also this one on quirksmode: Get Styles that shows the following function:
function getStyle(el,styleProp)
{
var x = document.getElementById(el);
if (x.currentStyle)
var y = x.currentStyle[styleProp];
else if (window.getComputedStyle)
var y = document.defaultView.getComputedStyle(x,null).getPropertyValue(styleProp);
return y;
}
This allows you to query for style properties

Styles override each other in the order in which they're defined: So anything in some_style3 that overrides the same selector in some_style2, say, will do. Otherwise, it will just be a union of the sets of selectors.
EDIT Some selectors won't override, but instead act relatively on a previous definition, so you've got to be careful about that.

How to dynamically set and modify CSS in JavaScript?

I have some JavaScript code that creates some div elements and it sets their CSS properties.
Because I would like to decouple CSS logic from my JavaScript code and because CSS is easier to read in its own .css file, I would like to set the CSS className of my element and then dynamically inject some values into the defined CSS property.
Here is what I would like to do :
style.css:
.myClass {
width: $insertedFromJS
}
script.js:
var myElement = document.createElement("div");
myElement.className = "myClass";
I want to do something like this but at that point myElement.style.width is empty
myElement.style.width.replaceAll("$insertedFromJS", "400px");
I think my problem here is that after the call to myElement.className = "myClass", the CSS is not yet applied.

If I understand your question properly, it sounds like you're trying to set placeholder text in your css file, and then use javascript to parse out the text with the css value you want to set for that class. You can't do that in the way you're trying to do it. In order to do that, you'd have to grab the content of the CSS file out of the dom, manipulate the text, and then save it back to the DOM. But that's a really overly-complicated way to go about doing something that...
myElement.style.width = "400px";
...can do for you in a couple of seconds. I know it doesn't really address the issue of decoupling css from js, but there's not really a whole lot you can do about that. You're trying to set css dynamically, after all.
Depending on what you're trying to accomplish, you might want to try defining multiple classes and just changing the className property in your js.

Setting the style, might be accomplished defining the inner-page style declaration.
Here is what i mean
var style = document.createElement('style');
style.type = 'text/css';
style.cssText = '.cssClass { color: #F00; }';
document.getElementsByTagName('head')[0].appendChild(style);
document.getElementById('someElementId').className = 'cssClass';
However the part of modifying it can be a lot of tricky than you think. Some regex solutions might do a good job. But here is another way, I found.
if (!document.styleSheets) return;
var csses = new Array();
if (document.styleSheets[0].cssRules) // Standards Compliant {
csses = document.styleSheets[0].cssRules;
}
else {
csses = document.styleSheets[0].rules; // IE
}
for (i=0;i<csses.length;i++) {
if ((csses[i].selectorText.toLowerCase()=='.cssClass') || (thecss[i].selectorText.toLowerCase()=='.borders'))
{
thecss[i].style.cssText="color:#000";
}
}

could you use jQuery on this? You could use
$(".class").css("property", val); /* or use the .width property */

There is a jQuery plugin called jQuery Rule,
http://flesler.blogspot.com/2007/11/jqueryrule.html
I tried it to dynamically set some div sizes of a board game. It works in FireFox, not in Chrome. I didn't try IE9.

changing css class model using JavaScript

Is it in any way possible, to change a css class model using JavaScript?
Pseudo code:
function updateClass(className, newData) {
cssInterface.alterClass(className, newData);
}
className being the name of the class, which is supposed to be changed (like ".footer") and newData being the new class content (like border: "1px solid pink;").
The target is, actually, just to save space: I am working with CSS3-animations, so changing one attribute of an element, which is affected by it's class, will terminate the animation of of it - The (in my case) font size won't change anymore. Using different classes will require an entire new set of classes for all affected elements, I'd like to avoid this.
I am not searching for a change via
element.className = "foo";
or
element.style.fontSize = "15pt";
Thanks for your help, guys :)

Here's my function to do this...
function changeCSS(typeAndClass, newRule, newValue) // modify the site CSS (if requred during scaling for smaller screen sizes)
{
var thisCSS=document.styleSheets[0] // get the CSS for the site as an array
var ruleSearch=thisCSS.cssRules? thisCSS.cssRules: thisCSS.rules // work out if the browser uses cssRules or not
for (i=0; i<ruleSearch.length; i++) // for every element in the CSS array
{
if(ruleSearch[i].selectorText==typeAndClass) // find the element that matches the type and class we are looking for
{
var target=ruleSearch[i] // create a variable to hold the specific CSS element
var typeExists = 1;
break; // and stop the loop
}
}
if (typeExists)
{
target.style[newRule] = newValue; // modify the desired class (typeAndClass) element (newRule) with its new value (newValue).
}
else
{
alert(typeAndClass + " does not exist.");
}
}
Called with (example)
changeCSS("div.headerfixed","-moz-transform-origin", "100% 0%");
hope this helps.

See my answer here. To answer your question: Yes, it's possible.
#CSS3: I tried exactly the same in one of my html5 experiments. I created an extra <style> element, and changed its contentText to the CSS class definitions I needed. Of course changing the cssRule object would be much cleaner :-)

As far as I can tell the CSS object model cannot easily tell you whether you already have an existing style rule for a particular class, but you can easily append a new rule for that class and it will override any previous declaration of that style.
I found an example of creating dynamic stylesheets.

You should take a look at dojo, it has some nice features where you can do just that..
require(["dojo/dom-class"], function(domClass){
// Add a class to some node:
domClass.add("someNode", "anewClass");
});
http://dojotoolkit.org/reference-guide/1.7/dojo/addClass.html