fix error with null document.body

[AndreyMiloserdov]

In some libraries used dom-helpers appear error:

matches.js:23 Uncaught TypeError: Cannot read property 'matches' of null
    at matches.js:23
    at Object.exports.__esModule (matches.js:28)
    at __webpack_require__

just replace code in dom-helpers/query/matches.js from

  if (_inDOM2.default) {
    (function () {
      var body = document.body;
      var nativeMatch = body.matches || body.matchesSelector || body.webkitMatchesSelector || body.mozMatchesSelector || body.msMatchesSelector;

      matches = nativeMatch ? function (node, selector) {
        return nativeMatch.call(node, selector);
      } : ie8MatchesSelector;
    })();
  }

to

document.addEventListener('DOMContentLoaded', function() {
  if (_inDOM2.default) {
    (function () {
      var body = document.body;
      var nativeMatch = body.matches || body.matchesSelector || body.webkitMatchesSelector || body.mozMatchesSelector || body.msMatchesSelector;

      matches = nativeMatch ? function (node, selector) {
        return nativeMatch.call(node, selector);
      } : ie8MatchesSelector;
    })();
  }
});

That fix problems for null document.body

[vdh]

I tried applying that fix but it failed the Karma tests.

This whole matches functionality is written synchronously around the idea that DOMContentLoaded has already fired. I can't think of a good way to fix it without rewriting the whole thing to properly wait asynchronously for DOMContentLoaded.

[jquense]

Yes you should either load scripts in the body per web best practices or do the content loaded handler at the root of your app

[vdh]

@jquense I know about best practices, but they shouldn't then get turned into silent hard dependencies.

I already have a DOMContentLoaded listener before the root of my app, but because this async dependency is happening at require time, this matches code is executing immediately, long before any React component code that actually needs to use it is fired… :(

[jquense]

Yes, there is basically a dependency that scripts not execute before the body because we need an element to do tests against. You don't need to wait for content loaded, moving the script tag to below the body will work as well. I'm happy to take a PR switching all checks to something more lazy and keeps the API the same. It may be easier tho to not load the script in the HEAD