How to Access CSS-Generated Content in JavaScript
Problem:
In CSS, counter and content properties generate custom content, such as figure numbering ("Fig. 1.1") for images. The question arises: how can this content be accessed programmatically using JavaScript?
Answer:
Accessing Live Counter Values
Unfortunately, there is no direct interface in JavaScript to access the live counter values generated by CSS. Attempts to retrieve them via getComputedStyle only return the values declared in the stylesheet, not the actual runtime values.
The DOM Level 2 Style Counter interface, which initially seemed promising, also lacks a property to retrieve the current counter value.
Alternative Approach
Since accessing the live counter values directly is not feasible, an alternative approach is to replicate the browser's own counter mechanism using JavaScript. The following script can be used:
window.onload = function () {
// Get all counter elements
var counters = Node_getElementsByClassName(document.body, 'counter');
// Initialize indices
var indices = [];
for (var counteri = 0; counteri < counters.length; counteri++) {
// Get counter level
var counter = counters[counteri];
var level = Element_getClassArgument(counter, 'level');
// Update indices
while (indices.length <= level) indices.push(0);
indices[level]++;
indices = indices.slice(level + 1);
// Create text node for figure number
var text = document.createTextNode('Figure ' + indices.join('.'));
// Insert figure number before counter element
counter.parentNode.insertBefore(text, counter.nextSibling);
// If counter has an ID, add figure number to links
if (counter.id !== '') {
for (var linki = document.links.length; linki > 0; linki--) {
var link = document.links[linki];
if (link.hostname === location.hostname && link.pathname === location.pathname && link.search === location.search && link.hash === '#' + counter.id) {
// Create text node for link number
var text = document.createTextNode('(' + indices.join('.') + ')');
// Insert link number after link
link.parentNode.insertBefore(text, link.nextSibling);
}
}
}
}
};
This script adds figure numbers to heading and figure elements and appends corresponding numbers to links referencing those headings and figures.
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