feat(dom): added snippet to clean up the page

Author: bahmutov

README.md

@@ -94,6 +94,8 @@ if your [exception handler](http://glebbahmutov.com/blog/catch-all-errors-in-ang
 
 * [github-pull-request-template.js](github-pull-request-template.js) - better GitHub pull request
 text, based on the blog post [Enforce standards while submitting a pull request](http://krasimirtsonev.com/blog/article/enforce-standards-while-submitting-a-pull-request) by [Krasimir Tsonev](https://github.com/krasimir).
+* [remove-all-but.js](remove-all-but.js) - removes all elements in the page, except the ones in
+the trees with specified selectors. Can be used to quickly clean up the page and leave just the essentials.
 
 All snippets, including mine are distributed under MIT license.
 
@@ -102,6 +104,9 @@ All snippets, including mine are distributed under MIT license.
 You can update local code snippets by downloading new versions from this github repository.
 Create a new code snippet and copy the source from [update-code-snippets.js](update-code-snippets.js).
 
+Note: the approach below does not work any more, 
+see [the open issue](https://github.com/bahmutov/code-snippets/issues/23).
+
 You will run this code snippet in an unusual way. First, open any web page, even an empty tab.
 Open the DevTools in **undocked** mode (Command+Option+I on Mac). Then open the DevTools **again**,
 *while focused* on the first DevTools. This will open the second DevTools instance with the source for the

remove-all-but.js

@@ -0,0 +1,52 @@
+/*
+Removes all elements except for the trees rooted
+in the given selectors.
+
+For example, given a document
+
+body
+  div.foo
+    span
+  div#bar
+    div#baz
+      hello
+
+and command with selectors ('.foo', '#baz') will leave
+everything in place, but command ('#baz') will leave just
+
+body
+  div#bar
+    div#baz
+      hello
+*/
+(function hideAllBut() {
+  function toArray(what) {
+    return Array.prototype.slice.call(what, 0);
+  }
+  const selectors = toArray(arguments);
+  if (!selectors.length) {
+    throw new Error('Need at least one selector to leave');
+  }
+
+  const keep = selectors.map(function (selector) {
+    return document.querySelector(selector);
+  });
+
+  function shouldKeep(el) {
+    return keep.some(function (keepElement) {
+      return keepElement.contains(el) || el.contains(keepElement);
+    });
+  }
+
+  const all = toArray(document.body.querySelectorAll('*'), 0);
+  var removed = 0;
+
+  all.forEach(function (el) {
+    if (!shouldKeep(el)) {
+      el.parentNode.removeChild(el);
+      removed += 1;
+    }
+  });
+
+  console.log('removed %d elements', removed);
+}('.foo', '#baz'));

utils/.jshintrc

@@ -30,7 +30,7 @@
   "debug"         : false,
   "eqnull"        : false,
   "es5"           : false,
-  "esnext"        : false,
+  "esnext"        : true,
   "moz"           : false,
   "evil"          : false,
   "expr"          : false,