Add support for line numbers

src/LineNumbers.js

@@ -0,0 +1,15 @@
+function LineNumbers(lineCount) {
+  let lineNumbersWrapper = "";
+  if (!lineCount) {
+    return lineNumbersWrapper;
+  }
+
+  const linesNum = lineCount;
+
+  const lines = new Array(linesNum + 1).join("<span></span>");
+  lineNumbersWrapper = `<span aria-hidden="true" class="line-numbers-rows">${lines}</span>`;
+
+  return lineNumbersWrapper;
+}
+
+module.exports = LineNumbers;

src/markdownSyntaxHighlight.js

@@ -1,6 +1,7 @@
 const Prism = require("prismjs");
 const PrismLoader = require("prismjs/components/index.js");
 const HighlightLinesGroup = require("./HighlightLinesGroup");
+const LineNumbers = require("./LineNumbers");
 
 module.exports = function(str, language) {
   if(!language) {
@@ -31,5 +32,15 @@ module.exports = function(str, language) {
     return highlights.getLineMarkup(j, line);
   });
 
-  return `<pre class="language-${language}"><code class="language-${language}">${highlightedLines.join("<br>")}</code></pre>`;
+
+  // Not sure how to configure this on/off
+  const numberLines = LineNumbers(highlightedLines.length);
+  const preClasses = [
+    `language-${language}`,
+  ];
+  if (numberLines !== "") {
+    preClasses.push("line-numbers");
+  }
+
+  return `<pre class="${preClasses.join(" ")}"><code class="language-${language}">${highlightedLines.join("<br>")}${numberLines}</code></pre>`;
 };