Emit a warning when white-space is left as normal on the editable ele…

…ment

Issue #62
Issue ProseMirror/prosemirror#981

src/domobserver.js

@@ -143,7 +143,10 @@ export class DOMObserver {
       }
     }
     if (from > -1 || newSel) {
-      if (from > -1) this.view.docView.markDirty(from, to)
+      if (from > -1) {
+        this.view.docView.markDirty(from, to)
+        checkCSS(this.view)
+      }
       this.handleDOMChange(from, to, typeOver)
       if (this.view.docView.dirty) this.view.updateState(this.view.state)
       else if (!this.currentSelection.eq(sel)) selectionToDOM(this.view)
@@ -192,3 +195,12 @@ export class DOMObserver {
     }
   }
 }
+
+let cssChecked = false
+
+function checkCSS(view) {
+  if (cssChecked) return
+  cssChecked = true
+  if (getComputedStyle(view.dom).whiteSpace == "normal")
+    console["warn"]("ProseMirror expects the CSS white-space property to be set, preferably to 'pre-wrap'. It is recommended to load style/prosemirror.css from the prosemirror-view package.")
+}