check if locale json file is valid or not (parsable and has unique jeys only) - since git merge may cause headaches

checkLocaleJsonValidity.js

const fs = require('fs');
const path = require('path');
const dir = path.join(__dirname, '/../locales');
fs.readdir(dir, (err, files) => {
  files.filter(fn => /\.json$/.test(fn)).forEach(fn => {
    fs.readFile(path.join(dir, fn), (err, s) => {
      s = s + '';
      let lang = {};
      try {
        lang = JSON.parse(s);
      } catch (err) {
        console.error(`JSON parse error in file "${fn}"`);
        throw err;
      }
      const line = s.replace(/[\r\n]/g, '');
      Object.keys(lang).forEach(key => {
        if (line.split(`"${key}":`).length > 2) {
          console.log(`Multiple keys in "${fn}": "${key}"`);
          throw new Error('JSON key not unique.');
        }
      });
    });
  });
});