(INCOMPLETE: ES6 Module conversion and linting)

- Breaking change: Require `new` with `EmbeddedSVGEdit` (allows us to use `class` internally)
- Breaking change: If `svgcanvas.setUiStrings` must now be called if not using editor in order
    to get strings (for sake of i18n) (and if using path.js alone, must also have its `setUiStrings` called)
- Breaking change (ext-overview-window): Avoid global `overviewWindowGlobals`
- Breaking change (ext-imagelib): Change to object-based encoding for namespacing of
    messages (though keep stringifying/parsing ourselves until we remove IE9 support)
- Breaking change: Rename `jquery.js` to `jquery.min.js`
- Breaking change: Remove `scoped` attribute from `style`; it is now deprecated and
    obsolete; also move to head (after other stylesheets)
- Enhancement: Make SpinButton plugin independent of SVGEdit via
    generic state object for tool_scale
- Enhancement: Remove now unused Python l10n scripts (#238)
- Enhancement: ES6 Modules (including jQuery plugins but not jQuery)
- Enhancement: Further JSDoc (incomplete)
- Enhancement (Optimization): Compress images using imageoptim (and add
    npm script) (per #215)
- Fix: i18nize path.js strings and canvas notifications
- Fix: Attempt i18n for ext-markers
- Refactoring (ext-storage): Move locale info to own file imported by the extension (toward modularity; still should be split into separate files by language and *dynamically* imported, but we'll wait for better `import` support to refactor this)
- Refactoring: For imagelib, add local jQuery copy (using old 1.4.4 as had
    been using from server)
- Refactoring: For MathJax, add local copy (using old 2.3 as had been using from
    server); server had not been working
- Refactoring: Remove `use strict` (implicit in modules)
- Refactoring: Remove trailing whitespace, fix some code within comments
- Refactoring: Expect `jQuery` global rather than `$` for better modularity
    (also to adapt line later once available via `import`)
- Refactoring: Prefer `const` (and then `let`)
- Refactoring: Add block scope keywords closer to first block in which they appear
- Refactoring: Use ES6 `class`
- Refactoring `$.isArray` -> `Array.isArray` and avoid some other jQuery core methods
    with simple VanillaJS replacements
- Refactoring: Use abbreviated object property syntax
- Refactoring: Object destructuring
- Refactoring: Remove `uiStrings` contents in svg-editor.js (obtains from locale)
- Refactoring: Add favicon to embedded API file
- Refactoring: Use arrow functions for brief functions (incomplete)
- Refactoring: Use `Array.prototype.includes`/`String.prototype.includes`;
    `String.prototype.startsWith`, `String.prototype.trim`
- Refactoring: Remove now unnecessary svgutils do/while resetting of variables
- Refactoring: Use shorthand methods for object literals (avoid ": function")
- Refactoring: Avoid quoting object property keys where unnecessary
- Refactoring: Just do truthy/falsey check for lengths in place of comparison to 0
- Refactoring (Testing): Avoid jQuery usage within most test files (defer script,
    also in preparation for future switch to ES6 modules for tests)
- Refactoring: Make jpicker variable declaration indent bearable
- Refactoring (Linting): Finish svgcanvas.js
- Docs: Mention in comment no longer an entry file as before
- Docs: Migrate old config, extensions, and FAQ docs
- Licensing: Indicate MIT is license type of rgbcolor; rename/add license file name for
    jgraduate and screencast to reflect type (Apache 2.0); rename file to reflect it
    contains license information (of type MIT) for Raphael icons

editor/extensions/imagelib/index.js

@@ -1,50 +1,47 @@
-/* eslint-disable no-var */
-/* globals $ */
+/* globals jQuery */
+const $ = jQuery;
 $('a').click(function () {
-  'use strict';
-  var metaStr;
-  var href = this.href;
-  var target = window.parent;
+  const {href} = this;
+  const target = window.parent;
+  const post = (message) => {
+    // Todo: Make origin customizable as set by opening window
+    // Todo: If dropping IE9, avoid stringifying
+    target.postMessage(JSON.stringify({
+      namespace: 'imagelib',
+      ...message
+    }), '*');
+  };
   // Convert Non-SVG images to data URL first
   // (this could also have been done server-side by the library)
-  if (this.href.indexOf('.svg') === -1) {
-    metaStr = JSON.stringify({
-      name: $(this).text(),
-      id: href
-    });
-    target.postMessage(metaStr, '*');
-
-    var img = new Image();
+  // Send metadata (also indicates file is about to be sent)
+  post({
+    name: $(this).text(),
+    id: href
+  });
+  if (!this.href.includes('.svg')) {
+    const img = new Image();
     img.onload = function () {
-      var canvas = document.createElement('canvas');
+      const canvas = document.createElement('canvas');
       canvas.width = this.width;
       canvas.height = this.height;
       // load the raster image into the canvas
       canvas.getContext('2d').drawImage(this, 0, 0);
       // retrieve the data: URL
-      var dataurl;
+      let data;
       try {
-        dataurl = canvas.toDataURL();
+        data = canvas.toDataURL();
       } catch (err) {
         // This fails in Firefox with file:// URLs :(
         alert('Data URL conversion failed: ' + err);
-        dataurl = '';
+        data = '';
       }
-      target.postMessage('|' + href + '|' + dataurl, '*');
+      post({href, data});
     };
     img.src = href;
   } else {
-    // Send metadata (also indicates file is about to be sent)
-    metaStr = JSON.stringify({
-      name: $(this).text(),
-      id: href
-    });
-    target.postMessage(metaStr, '*');
     // Do ajax request for image's href value
     $.get(href, function (data) {
-      data = '|' + href + '|' + data;
-      // This is where the magic happens!
-      target.postMessage(data, '*');
+      post({href, data});
     }, 'html'); // 'html' is necessary to keep returned data as a string
   }
   return false;