improve copying from code blocks

Set a `copy` event handler on "SCodeFlow" elements to perform a text
copy that strips away double newlines. This improves copying in
Firefox and Chrome, and it doesn't seem to hurt Safari.

Author: mflatt

scribble-lib/scribble/manual-racket.js

@@ -15,6 +15,24 @@ AddOnLoad(function() {
     }
 })
 
+// for copies that start in Racket code, strip out extra newlines
+AddOnLoad(function() {
+  const codeBlocks = document.getElementsByClassName("SCodeFlow");
+  for (var i = 0; i < codeBlocks.length; i++) {
+    var codeBlock = codeBlocks[i];
+    console.log("add");
+    codeBlock.addEventListener('copy', function(e) {
+      var selection = window.getSelection();
+      var text = selection.toString();
+      var codeText = text.replace(/\n\n/g, '\n');
+      if (text != codeText) {
+        e.preventDefault();
+        e.clipboardData.setData('text/plain', codeText);
+      }
+    })
+  }
+})
+
 // cache of source urls
 var cache = {};