Adjust `theme-color` as the class and theme of the page are switched

Question

Adjust `theme-color` as the class and theme of the page are switched

My website has a JavaScript toggle that changes the color/theme of the page by adding/removing classes on the html element. The default theme is white, the second theme is black (.dark-mode), and the third theme is beige (.retro).

The JavaScript code for the toggle has been simplified below:

const html = document.querySelector("html");
const button = document.querySelector(".contrast__link");

button.addEventListener("click", (e) => {
    e.preventDefault();
    if (html.classList.contains("dark-mode")) {
        html.classList.remove("dark-mode");
        html.classList.add("retro");
    } else if (html.classList.contains("retro")) {
        html.classList.remove("retro");
    } else {
        html.classList.add("dark-mode");
    }
});

After the class/theme updates, I want to update the theme-color in the document head to match the new color scheme. Initially, it was set as:

<meta name="theme-color" content="#ffffff">

I attempted using CSS variables hoping it would dynamically change the color:

CSS

:root       { --color-secondary : rgb(255,255,255); }
.dark-mode  { --color-secondary : rgb(0,0,0); }
.retro      { --color-secondary : rgb(243, 238, 226); }

Tag

<meta name="theme-color" content="var(--color-primary">

Unfortunately, it seems this method is not supported. Is there a way for the theme-color to be inherited or does it have to be a fixed value?

javascript html css meta-tags

Answer 1

Answer №1

It is accurate that the content attribute does not have support for CSS variables.

To adjust this value according to your theme, JavaScript will need to be utilized.

const html = document.querySelector("html");
const button = document.querySelector(".contrast__link");

// Begin by defining the colors for each theme
const colors = {
  default: '#ffffff', // color for the default theme
  darkMode: '#000000', // color for the dark-mode theme
  retro: '#f3eee2' // color for the retro theme
}

// Locate the meta tag
const metaThemeColor = document.querySelector("meta[name=theme-color]");

button.addEventListener("click", (e) => {
  e.preventDefault();
  if (html.classList.contains("dark-mode")) {
    html.classList.remove("dark-mode");
    html.classList.add("retro");
    // update the theme-color meta tag
    metaThemeColor.setAttribute('content', colors.retro);
  } else if (html.classList.contains("retro")) {
    html.classList.remove("retro");
    // update the theme-color meta tag
    metaThemeColor.setAttribute('content', colors.default);
  } else {
    html.classList.add("dark-mode");
    // update the theme-color meta tag
    metaThemeColor.setAttribute('content', colors.darkMode);
  }
});

Answer 2

It is accurate that the content attribute does not have support for CSS variables.

To adjust this value according to your theme, JavaScript will need to be utilized.

const html = document.querySelector("html");
const button = document.querySelector(".contrast__link");

// Begin by defining the colors for each theme
const colors = {
  default: '#ffffff', // color for the default theme
  darkMode: '#000000', // color for the dark-mode theme
  retro: '#f3eee2' // color for the retro theme
}

// Locate the meta tag
const metaThemeColor = document.querySelector("meta[name=theme-color]");

button.addEventListener("click", (e) => {
  e.preventDefault();
  if (html.classList.contains("dark-mode")) {
    html.classList.remove("dark-mode");
    html.classList.add("retro");
    // update the theme-color meta tag
    metaThemeColor.setAttribute('content', colors.retro);
  } else if (html.classList.contains("retro")) {
    html.classList.remove("retro");
    // update the theme-color meta tag
    metaThemeColor.setAttribute('content', colors.default);
  } else {
    html.classList.add("dark-mode");
    // update the theme-color meta tag
    metaThemeColor.setAttribute('content', colors.darkMode);
  }
});

Answer 3

Answer №2

This snippet of JavaScript code serves the purpose of updating the theme-color meta tag in an HTML document dynamically based on the background color of the body element. Let's dissect the functionality of each component within the code:

// Function to fetch the computed background color of the body element
function updateThemeColor() {
    var bgColor = window.getComputedStyle(document.body, null).getPropertyValue('background-color');
    
    // Locating the meta tag with name="theme-color"
    var metaTag = document.querySelector('meta[name="theme-color"]');
    
    // Updating content attribute of the meta tag with the retrieved background color
    if (metaTag) {
       metaTag.setAttribute('content', bgColor);
    } else {
        // Creating a new meta tag if it doesn't exist and appending it to the head element
        var newMetaTag = document.createElement('meta');
        newMetaTag.name = "theme-color";
        newMetaTag.content = bgColor;
        document.getElementsByTagName('head')[0].appendChild(newMetaTag);
    }
}

// Calling updateThemeColor once DOM content is fully loaded
document.addEventListener("DOMContentLoaded", updateThemeColor);

// Periodically updating the theme color meta tag every 100 milliseconds
setInterval(updateThemeColor, 100);

Explanation:

updateThemeColor() function:
- Retrieves the calculated background color of the body element utilizing
```
window.getComputedStyle(document.body, null).getPropertyValue('background-color')
```
  .
- Ensures retrieval of the actual background color defined through stylesheets or inline styles.
Finding or creating the meta tag:
- Utilizes
```
document.querySelector('meta[name="theme-color"]')
```
  to search for an existing meta tag named theme-color.
- If found (metaTag not being null), updates its content attribute to match the current bgColor.
- If not found, generates a new meta tag (newMetaTag) carrying a name="theme-color" and sets its content to bgColor. Then appends this fresh tag to the document's head element (
```
document.getElementsByTagName('head')[0].appendChild(newMetaTag)
```
  ).
Event listener and interval:
- ```
document.addEventListener("DOMContentLoaded", updateThemeColor);
```
  guarantees that updateThemeColor executes once the DOM content is fully loaded, initiating the theme-color.
- ```
setInterval(updateThemeColor, 100);
```
  schedules updateThemeColor to run every 100 milliseconds, continuously refreshing the theme-color meta tag to mirror dynamic changes in background color.

Purpose:

The primary intention behind this script usually lies within web applications or websites that alter their themes or background colors dynamically. The theme-color meta tag aids browsers and certain platforms (such as Android's Chrome) in adjusting the browser's UI to align with the website's color scheme, enhancing user experience and visual harmony.

Answer 4

This snippet of JavaScript code serves the purpose of updating the theme-color meta tag in an HTML document dynamically based on the background color of the body element. Let's dissect the functionality of each component within the code:

// Function to fetch the computed background color of the body element
function updateThemeColor() {
    var bgColor = window.getComputedStyle(document.body, null).getPropertyValue('background-color');
    
    // Locating the meta tag with name="theme-color"
    var metaTag = document.querySelector('meta[name="theme-color"]');
    
    // Updating content attribute of the meta tag with the retrieved background color
    if (metaTag) {
       metaTag.setAttribute('content', bgColor);
    } else {
        // Creating a new meta tag if it doesn't exist and appending it to the head element
        var newMetaTag = document.createElement('meta');
        newMetaTag.name = "theme-color";
        newMetaTag.content = bgColor;
        document.getElementsByTagName('head')[0].appendChild(newMetaTag);
    }
}

// Calling updateThemeColor once DOM content is fully loaded
document.addEventListener("DOMContentLoaded", updateThemeColor);

// Periodically updating the theme color meta tag every 100 milliseconds
setInterval(updateThemeColor, 100);

Explanation:

updateThemeColor() function:
- Retrieves the calculated background color of the body element utilizing
```
window.getComputedStyle(document.body, null).getPropertyValue('background-color')
```
  .
- Ensures retrieval of the actual background color defined through stylesheets or inline styles.
Finding or creating the meta tag:
- Utilizes
```
document.querySelector('meta[name="theme-color"]')
```
  to search for an existing meta tag named theme-color.
- If found (metaTag not being null), updates its content attribute to match the current bgColor.
- If not found, generates a new meta tag (newMetaTag) carrying a name="theme-color" and sets its content to bgColor. Then appends this fresh tag to the document's head element (
```
document.getElementsByTagName('head')[0].appendChild(newMetaTag)
```
  ).
Event listener and interval:
- ```
document.addEventListener("DOMContentLoaded", updateThemeColor);
```
  guarantees that updateThemeColor executes once the DOM content is fully loaded, initiating the theme-color.
- ```
setInterval(updateThemeColor, 100);
```
  schedules updateThemeColor to run every 100 milliseconds, continuously refreshing the theme-color meta tag to mirror dynamic changes in background color.

Purpose:

The primary intention behind this script usually lies within web applications or websites that alter their themes or background colors dynamically. The theme-color meta tag aids browsers and certain platforms (such as Android's Chrome) in adjusting the browser's UI to align with the website's color scheme, enhancing user experience and visual harmony.

Adjust `theme-color` as the class and theme of the page are switched

Answer №1

Answer №2

Explanation:

Purpose:

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