Use fat arrow functions const foo = () => { ... }; for callbacks

and any other function that is passed around and it's not a top level function

po/xgettext-html

@@ -89,7 +89,7 @@ for (let i = 0; i < opt.argv.length; i++) {
     const dom = new jsdom.JSDOM(file, { includeNodeLocations: true });
     const body = dom.window.document.body;
 
-    const locator = function (elem) {
+    const locator = (elem) => {
         const offset = dom.nodeLocation(elem).startOffset;
         const line = file.slice(0, offset).split("\n").length;
         return fn + ":" + line;