Apply CSS dynamically with JavaScript

Question

What is a good way to apply styling dynamically (i.e. the value of styles are created at runtime) to HTML elements with JavaScript?

I'm looking for a way to package a JavaScript widget (JS, CSS and markup) in a single component (basically, an object). The idea would be for the component to encapsulate styling (so users have a nice API to modify it instead of a more tightly coupled approach of modifying the CSS directly and having changes applied indirectly). The problem is that a single API call might imply changes to several styling elements.

The way I would do it is to construct the CSS and set thestyle atrribute to the proper elements (most likely using the ID to avoid applying changes to other areas of the markup). Is this a good solution? Is there a better way to do it?

Answer 1

Using Jquery

Use the css() function to apply style to existing elements where you pass an object containing styles :

var styles = {
  backgroundColor : "#ddd",
  fontWeight: ""
};
$("#myId").css(styles);

You can also apply one style at the time with :

$("#myId").css("border-color", "#FFFFFF");

Vanilla JS :

var myDiv = document.getElementById("#myId");
myDiv.setAttribute("style", "border-color:#FFFFFF;");

With Css :

You can also use a separate css file containing the different styles needed inside classes, and depending on the context you add or remove those classes to your elements.

in your css file you can have classes like

.myClass {
    background-color: red;
}

.myOtherClass {
    background-color: blue;
}

Again using jquery, to add or remove a class to an element, you can use

$("#myDiv").addClass('myClass');

or

$("#myDiv").removeClass('myClass');

Again, you can also do the same with vanilla JS:

document.getElementById("#myId").classList.add('myClass') 

or

document.getElementById("#myId").classList.remove('myClass') 

I think this is a cleaner way as it separates your style from your logic. But if the values of your css depends from what is returned by the server, this solution might be difficult to apply.

Answer 2

The way I would do it is to construct the CSS and set the style attribute to the proper elements. For example:

var div = document.createElement('div');
div.setAttribute("style", "color: blue, margin-top:5px");
document.body.appendChild(div);

This code will create a new div element with the style color: blue, margin-top:5px and append it to the page.

Answer 3

Using Vanilla JS you could do something like this.

If you want to add a CSS class named animate to an element with Id circle, do it like this.

var circle = document.getElementById("circle");
circle.classList.add('animate');

You can remove the class like this.

circle.classList.remove('animate');

Answer 4

Since you have also asked if there is a better way and you building a component, a better way i would recommend is for you to build such a component with frontend javascript framework because they make dynamically styles very easy out of the box take an example of Vuejs, Reactjs

`      
import React, {Component} from 'react'
import styled from 'styled-jss'
const Circle = styled('div')({
  position: 'absolute',
  width: 50,
  height: 50,
  borderRadius: '50%',
  background: (props) => (
    /* Generates a random or based on props color */
  ),
  transform: (props) => (
    /* Generates a random or based on props transform for  positioning */
  )
})
class Demo extends Component {
  componentDidMount() {
    this.tick()
  }
  tick = () => {
    requestAnimationFrame(() => {
      this.setState({/* Some new state */}, this.tick)
    })
  }
  render() {
    return (
      <div>
        {[...Array(amount)].map(() => <Circle />)}
      </div>
    )
  }
}
`

Answer 5

I could be misinterpreting your question, but it sounds like you are asking for a simple architectural pattern. You want something that makes it easier for someone who is using your widget to change it to their specifications?

If this is the case, then I do not know of any special pattern to do this without using CSS.

I can tell you that the "widgets" that I have found easiest to use do have separate CSS files. I have found it fairly straightforward to modify them to my needs. I think this is because the structure of using CSS with HTML and Javascript is already a nice, simple pattern. I don't know of there is anything better, especially considering that people are already very familiar with the HTML/CSS relationship.

Answer 6

window.onscroll = function(){workOnScroll()};
function workOnScroll() {
  if (document.body.scrollTop > 50 || document.documentElement.scrollTop > 50) {
      var ul = document.getElementById("ulID");
      ul.setAttribute("style", "position: sticky;top: 150px;");
  } else {
      var ul = document.getElementById("ulID");
      ul.setAttribute("style", "position: relative;top: 0px;");
  }
}