discourse/documentation/chat/frontend/scripts/prism-linenumbers.js

(function() {

if (typeof self === 'undefined' || !self.Prism || !self.document) {
  return;
}

Prism.hooks.add('complete', function (env) {
  if (!env.code) {
    return;
  }

  // works only for <code> wrapped inside <pre> (not inline)
  var pre = env.element.parentNode;
  var clsReg = /\s*\bline-numbers\b\s*/;
  if (
    !pre || !/pre/i.test(pre.nodeName) ||
      // Abort only if nor the <pre> nor the <code> have the class
    (!clsReg.test(pre.className) && !clsReg.test(env.element.className))
  ) {
    return;
  }

  if (env.element.querySelector(".line-numbers-rows")) {
    // Abort if line numbers already exists
    return;
  }

  if (clsReg.test(env.element.className)) {
    // Remove the class "line-numbers" from the <code>
    env.element.className = env.element.className.replace(clsReg, '');
  }
  if (!clsReg.test(pre.className)) {
    // Add the class "line-numbers" to the <pre>
    pre.className += ' line-numbers';
  }

  var match = env.code.match(/\n(?!$)/g);
  var linesNum = match ? match.length + 1 : 1;
  var lineNumbersWrapper;

  var lines = new Array(linesNum + 1);
  lines = lines.join('<span></span>');

  lineNumbersWrapper = document.createElement('span');
  lineNumbersWrapper.setAttribute('aria-hidden', 'true');
  lineNumbersWrapper.className = 'line-numbers-rows';
  lineNumbersWrapper.innerHTML = lines;

  if (pre.hasAttribute('data-start')) {
    pre.style.counterReset = 'linenumber ' + (parseInt(pre.getAttribute('data-start'), 10) - 1);
  }

  env.element.appendChild(lineNumbersWrapper);

});

}());