I am using Polymer 2 to build a library of components, but I am having issues with css variables in browsers other than Chrome.
I have a wrapper component (x-page) and it has a theme property that can be either light or dark. My css looks similar to this:
:host([light]) {
---color-1: rgb(200,200,200);
---color-2: rgb(210,210,210);
}
:host([dark]) {
---color-1: rgb(10,10,10);
---color-2: rgb(20,20,20);
}
I now want to use these variables in all components inside this wrapper (not only directly slotted, all of them including their shadow-root.
In Chrome this works fine, as the children will read the variables from the wrapper, but in other browsers it doesn't seem to work even though I am using the apply-shim polyfill and tried with the custom-styles as well.
I appreciate your help :)
In order that CSS styles can be applied with the Shadow DOM polyfill, at first you must prepare the <template> you append to the shadow root with the ShadyCSS.prepareTemplate() function, as explained in the ShadyCSS polyfill page:
ShadyCSS.prepareTemplate( template1, 'x-page' )
Example:
ShadyCSS.prepareTemplate( template1, 'x-page' )
class XPage extends HTMLElement {
constructor() {
super()
this.attachShadow( { mode: "open" } )
.appendChild( template1.content.cloneNode( true ) )
}
}
customElements.define( 'x-page', XPage )
<script src="https://rawgit.com/webcomponents/webcomponentsjs/master/webcomponents-bundle.js"></script>
<template id="template1">
<style>
:host([light]) {
---color-1: red;
---color-2: pink;
}
:host([dark]) {
---color-1: yellow;
---color-2: black;
}
span {
color: var(---color-1);
background-color: var(---color-2);
}
</style>
<span><slot></slot></span>
</template>
<x-page light>Light</x-page>
<x-page dark>Dark</x-page>
Related
In a project I'm working on, I have this LitElement component, which is absolute-positioned and determines its left or top locations according to its reactive properties.
I've encountered a problem in Safari only, including iOS Safari/Chrome/Firefox. The element has updated its shadow styles, but in the view it does not move at all. I realized its a render issue when I found that when the cursor hovers the element, or exits the browser view, the element pops to the expected location.
I managed to reproduce the problem with a simpler code:
my-elem.ts:
import { LitElement, html, property, customElement, css } from 'lit-element';
#customElement('my-elem')
export class MyElem extends LitElement {
#property({ type: Number, reflect: true })
left: number = 30
static get styles() {
return css`
:host { position: absolute; }
div { position: absolute; }
`;
}
render() {
return html`
<style>
:host { left: ${this.left}px; }
</style>
<div> Hello </div>
`;
}
}
index.html:
<html lang="en">
<head>
<script src="my-elem.ts"></script>
</head>
<body>
<my-elem id="my-elem" left="50"></my-elem>
<button id="move-btn">move</button>
<script>
const elem = document.getElementById('ma-elem');
const moveBtn = document.getElementById('move-btn');
moveBtn.onclick = function() {
elem.left += 30;
}
</script>
</body>
</html>
I found that this happens only on :host selector. If the shadowed styling updates the div's left, it renders without any problems.
I wish to avoid forcing the browser to layout/paint, due to performance issues.
I think the root of your problem is that you are trying to use an expression inside a style element in your render template.
The LitElement guide mentions that using them that way has limitations and can cause performance issues. I think your problem is just facing one of them so you should remove that style element.
As an alternative, since you want to affect the host element, you can actually do this in an easier way if you just don't use a property but style the host directly.
So when using my-elem the code would look like:
<my-elem style="left: 30px;"></my-elem>
This is because styles applied to :host in shadow DOM have less priority than those applied to it using classes or the style attribute by its parent.
Alternatively, if you really want to keep the property, you can create property accessors for the left property and set the style to the host from there like this:
export class MyElem extends LitElement {
// other code
set left(value) {
const oldValue = this.left;
this._left = value;
this.style.setProperty('left', `${value}px`)
this.requestUpdate('left', oldValue);
}
get left() {
return this._left;
}
}
How can I add separate CSS for one page in Angular?
This is the CSS I need, as per How to remove the URL from the printing page?:
#media print{
#page{
margin:0;
}
body{
margin:30px;
}
}
But putting CSS into the component with ::ng-deep or ViewEncapsulation.None won't help here, because when navigating away from a page, the CSS of the page isn't deleted.
I've added a Stackblitz, which explains the problem clearly.
I've come up with a potential solution, but it doesn't work:
encapsulation: ViewEncapsulation.None
...
constructor(private renderer: Renderer2) {
this.renderer.addClass(document.body, 'special-print');
}
ngOnDestroy() {
this.renderer.removeClass(document.body, 'special-print');
}
....
....
....
#media print{
#page{
margin:0;
}
body.special-print{
margin:30px;
}
}
Why it doesn't work:
While it would help with <body> CSS, it won't help with #page CSS. Perhaps the question would be better summarized as "How to add global CSS, but remove it when we leave the page?".
Solved!
We print the <style> block directly into the component's HTML, and therefore when the component gets removed, our <style> block gets removed too. (Normally this wouldn't work, but thanks to DomSanitizer.bypassSecurityTrustHtml, Angular won't break our code when running optimizations.)
Here's a StackBlitz.
First, create a new component to handle the work:
component.ts: (This is all we need. We don't need an HTML or style.css file.)
//Inside your local component, place this HTML
//<app-local-css [style]="'body{background:green !important;}'"></app-local-css>
// OR
//<app-local-css [scriptURL]="'/path/to/file.css'"></app-local-css>
#Component({
selector: "app-local-css",
template: '<span style="display:none" [innerHTML]="this.safeString"></span>'
})
export class LocalCSSComponent implements OnInit {
constructor(protected sanitizer: DomSanitizer) {}
#Input() scriptURL?: string;
#Input() style?: string;
safeString: SafeHtml;
ngOnInit() {
if (this.scriptURL) {
let string = '<link rel="stylesheet" type="text/css" href="' + this.scriptURL + '">';
this.safeString = this.sanitizer.bypassSecurityTrustHtml(string);
} else if (this.style) {
let string = '<style type="text/css">' + this.style + "</style>";
this.safeString = this.sanitizer.bypassSecurityTrustHtml(string);
}
}
}
And then use it like this:
mySample.component.html:
<app-local-css [style]="'body{background:green !important;}'"></app-local-css>
// OR
<app-local-css [scriptURL]="'/path/to/file.css'"></app-local-css>
Angular is doing client-side rendering, which is bad news, because you do not have separate pages. You have several possible solutions though:
1. Separate page
You can create another page with or without Angular, which includes the CSS you need and load that page. In the most simplistic approach to achieve this, the other page would have a different URL. If having a different URL is not to your liking, then you could hide your page's content and show the other page inside an iframe. It would admittedly be a hacky solution, but it is a solution.
2. Client-side CSS rendering
Instead of just loading the CSS, you could have a component which would control global CSS rules, matched by your view's name. You would have a template value rendered to a property, like:
#media print{
#page{
margin:0;
}
body{
margin:30px;
}
}
And when you visit the page where this needs to be activated, you would simply initialize a property with a style HTML element that was generated based on the template and added to head. Once you leave the given view, your component would detect that event and would remove() that element. If you choose this solution, then it would be wise to make sure that you are supporting this on more general terms, so that if some new views will have their custom global CSS, then they would be easy to integrate into your project in the future.
3. body classes
You could add/remove some custom-print or whatever class to/from body whenever the style is to be changed. This way you could add the CSS exactly once to your HTML and change the rules accordingly, like:
body.custom-print {
margin: 30px;
}
This would be a neat solution, but the problem in your case is that you have a #page rule as well and I'm not sure how you could make that dependant on body classes or some other HTML attributes. I would conduct quite a few experiments about this if I were you.
4. Iframe staging
You could avoid having that CSS in your main page, but would have a hidden iframe where you would have the CSS and would just copy the content into the CSS and once that's loaded, print that.
Don't change the whole body from apple. Instead, there are a few changes to make.
In the app component, hold a boolean for whether or not you are on apple, and use ngClass for class defined in scss.
Track which route you are on in appComponent, and set isApple accordingly
Add a div around all your html, for container to take full size
Add global html, body setting height to 100% so you see color everywhere
Remove body overriding in apple
so,
appComponent.ts:
isApple: Boolean;
constructor(router: Router) {
router.events.subscribe(v => {
if (v instanceof NavigationEnd) {
this.isApple = v.url === "/apple";
}
});
}
appComponent.html:
<div [ngClass]="{'red':isApple}" class="container">
<p>
There are two components: Apple and Banana. Switching between them will show
the problem.
</p>
<router-outlet></router-outlet>
</div>
appComponent.scss
.red {
background-color: red;
}
.container {
height: 100%;
}
apple.component.scss (remove body)
/*Sample "global" CSS, that affects something outside the current component.*/
::ng-deep {
#media print {
#page {
margin: 0;
}
}
}
styles.scss (global)
html, body {
height: 100%;
}
You can see this altogether at this Stackblitz link
You can add different css files in the component (for instance, app-task.component.ts):
#Component({
selector: 'app-task',
templateUrl: './app-task.component.html',
styleUrls: ['./app-task.component.scss', './styles2.scss', './styles3.scss']
})
In this example, the style files are in the same folder that the component, but this is not the best option: you have to put the files in assets, for example. Also, be careful with the thread of the styles, since the first one you put will be put before the second (obviously).
I'm using the follow web-component tree:
<x-typography>
:shadow-root
<x-select>
:shadow-root
<div class="select-container>
</div>
</x-select>
</x-typography>
And I need to override the background-color on select-container. I don't have access to <x-select> code, only <x-typography>.
I know how to :host and ::slotted works, I tried:
:host(x-typography):host(x-select) .select-container
:host(x-typography):host(x-select) .select-container
:host(x-typography :host(x-select)) .select-container
But none of them work.
You can use the ::part pseudo-element and exportparts attribute for this. It allows you to make custom styles for inner Shadow DOM element.
You can specify a "styleable" part on any element in your shadow tree:
<x-select>
:shadow-root
<header class="select-header"></header>
<div class="select-container" part="container"></div>
</x-select>
And then you can specify custom styles for that part like:
x-select::part(container){
font-weight: bold;
}
Also it works with other pseudo selectors like :hover, :active...
x-select::part(container):hover {
opacity: 0.8;
}
But it doesn't work with nested parts. So, you cannot use it like:
x-select::part(container)::part(aside) {
}
For that purpose you need to export the part via exportpart attribute.
<x-bar>
:shadow-root
<x-foo exportparts="some-box: foo-some-box"></x-foo>
</x-bar>
However, if you need to support IE11 then it might be not the best option. From the other hand, it's supported by all modern browsers: https://caniuse.com/#search=%3A%3Apart
So, your example would look like:
// x-select
render () {
return (
<Host>
<div class="select-container" part="container"></div>
</Host>
)
}
// x-typography
render () {
return (
<Host>
<x-select exportparts="container: container"></x-select>
</Host>
)
}
<!-- usage -->
<x-typography></x-typography>
<style>
x-typography::part(container) {
color: blue;
}
</style>
Here you can find a great explanation how part works: https://github.com/fergald/docs/blob/master/explainers/css-shadow-parts-1.md
Let's assume that the user can add styles for every component in admin panel and I get it as string in my Node server:
const stylesFromAPI = ".p { color: red } .bg { background: lime }";
How to prefix this styles before append to my document to avoid conflicts?
I need something like CSS modules but working with strings (not as module loader):
const stylesFromAPI = css(".p { color: red } .bg { background: lime }"); // returns hashedClassname685946898456
<SomeCompontent className={stylesFromAPI} />
produces:
<style>
.hashedClassname685946898456 .p { color: red }
.hashedClassname685946898456 .bg { background: lime }
</style>
<div class="hashedClassname685946898456"></div>
Shadow DOM seems like a reasonable option here. You can create your style tags with inside the shadow DOM without having to deal with any selector prefixes. For example, using the react-shadow package:
import root from 'react-shadow';
Then in JSX, something like:
<root.div>
<style type="text/css">
{/* CSS string here */}
</style>
<div>
{/* Stuff here */}
</div>
</root.div>
Check out a working example of this here: https://github.com/joshdavenport/stack-overflow-61566764-react-css-shadow-dom
The main downside here is your styles from outside the shadow DOM will not apply. Those using the shadow DOM for components see this as a good thing, those simply trying to scope CSS do not. Not sure what it is you're scoping, so I can't really tell if that would be an issue for you.
If it is, you could re-import your styles within the shadow DOM, though I can't really point out how to do that without knowing what bundler is in use and how it is in use.
Alternatively you could pull apart your imported CSS using the css package, iterate over the selectors prefixing all with a randomly generated class, and then re-stringify.
I have a very wierd question, I dont know wether if its possible in css or not
Suppose I have say 3 different css classes as shown below, as you can see I have a common property of all these classes, I want to declare this color somewhere else and pass a reference to it here, so if next time I want to change the color I can simply change at one place rather than changing in all the 5 classes.
I know that you can use body{}, or a wrapper for this but that would affect the colors of the entire site right ? Is there a way to do this ?
Is this even possible ?
.abc {
color:red;
}
.abc2 {
color:red;
}
.abc3 {
color:red;
}
.abc4 {
color:red;
}
.abc5 {
color:red;
}
The bad news: you can't do it in CSS.
The good news: you can write in a meta-CSS language like LESS, which then processes a LESS file to pure CSS. This is called a "mixin".
In LESS:
#errorColor: red;
.error-color {
color: #errorColor;
}
#error-1 {
.error-color;
}
.all-errors {
.error-color;
}
More info: http://lesscss.org/#-mixins
if you want to declare all of them at a time, you can use:
.abc, .abc2, .abc3, .abc4, .abc5 {
color:red;
}
Or you can declare an additional class & add to all the .abc, .abc2.... & make its color:red;.
This can not be done with CSS, but that is still a very popular thing to do by using a CSS preprocessor such as LESS, SASS, SCSS, or Stylus.
A preprocessor will let you define a variable (say $red = #F00). It will replace the variable in your CSS document with the variable value for you, allowing you to write very DRY and module CSS.
This functionality is referred to as "CSS variables", which is part of the future spec, but not yet implemented on any browsers.
For now, the best way to do this in pure CSS is to declare an additional class for the desired "global", and then add that class to all relevant items.
.abc_global { color: red; }
.abc1 { /* additional styling */ }
.abc2 { /* additional styling */ }
<div class="abc1 abc_global"></div>
<div class="abc2 abc_global"></div>
With LESS
You are able to define that red color once:
.myRedColor {
color:red;
}
Now you can call that red on any CSS styles. Even NESTED styles! It's a wicked tool!
.abc1 {
.myRedColor;
}
.abc2 {
.myRedColor;
}
.abc3 {
.myRedColor;
}
.abc4 {
.myRedColor;
}
NESTED EXAMPLE:
.abc {
.itsEasyAsOneTwoThree{
.myRedColor;
}
}
Now all of our "itsEasyAsOneTwoThree" classes that are properly nested inside of an "abc" class will be assigned the red style. No more remembering those long #867530 color codes :) How cool is that?!
You can also use PostCSS with the plugin postcss-preset-env and support custom properties/variables, then use the :root selector to add global css variables.
:root {
--color-gray: #333333;
--color-white: #ffffff;
--color-black: #000000;
}