build-modules-support.js

const path = require("path");
const fs = require("fs");

const compatData = require("mdn-browser-compat-data").javascript;

// Map mdn-browser-compat-data to browserslist browser names
const browserNameMap = {
  chrome_android: "and_chr",
  firefox_android: "and_ff",
  safari_ios: "ios_saf",
  nodejs: "node",
  webview_android: "android",
  opera_android: "op_mob",
  samsunginternet_android: "samsung",
};

const browserSupportMap = {
  android: "chrome_android", // map to chrome here as Android WebView 61 is Chromium-based
};

function browserVersion(browser, version_added) {
  if (browser === "samsunginternet_android" && version_added === "8.0") {
    return "8.2"; // samsung 8.0 is not defined in browserslist
  }
  // fixme: preset-env maps opera_android as opera, this is incorrect as they have different engine mappings
  // see https://github.com/mdn/browser-compat-data/blob/master/browsers/opera_android.json
  if (browser === "opera_android" && version_added === "45") {
    return "48";
  }
  return version_added;
}

function process(source) {
  const stats = source.__compat.support;
  const allowedBrowsers = {};

  Object.keys(stats).forEach(browser => {
    const browserName = browserNameMap[browser] || browser;
    let browserSupport = stats[browserSupportMap[browserName] || browser];
    if (Array.isArray(browserSupport)) {
      browserSupport = browserSupport[0]; // The first item is the most progressive support
    }
    if (browserSupport.version_added && !browserSupport.flags) {
      allowedBrowsers[browserName] = browserVersion(
        browser,
        browserSupport.version_added
      );
    }
  });

  return allowedBrowsers;
}

const dataPath = path.join(__dirname, "../data/native-modules.json");
const data = {
  "es6.module": process(compatData.statements.export),
};
fs.writeFileSync(dataPath, `${JSON.stringify(data, null, 2)}\n`);
exports.process = process;