Editor only does not pre-build lines, it only builds them when they are visible on the screen

spec/app/editor-spec.coffee

@@ -25,8 +25,8 @@ describe "Editor", ->
     editor = rootView.activeEditor()
     buffer = editor.buffer
 
-    editor.attachToDom = (options={}) ->
-      heightInLines = options.heightInLines ? this.buffer.numLines()
+    editor.attachToDom = ({ heightInLines } = {}) ->
+      heightInLines ?= this.buffer.numLines()
       this.height(getLineHeight() * heightInLines)
       $('#jasmine-content').append(this)
 
@@ -60,7 +60,7 @@ describe "Editor", ->
       expect(newEditor.editSessions[0]).toEqual(editor.editSessions[0])
       expect(newEditor.editSessions[0]).not.toBe(editor.editSessions[0])
 
-    describe ".setBuffer(buffer)", ->
+  describe ".setBuffer(buffer)", ->
     it "sets the cursor to the beginning of the file", ->
       expect(editor.getCursorScreenPosition()).toEqual(row: 0, column: 0)
 
@@ -392,7 +392,7 @@ describe "Editor", ->
           otherEditor.simulateDomAttachment()
           expect(otherEditor.setMaxLineLength).toHaveBeenCalled()
 
-    fdescribe "when some lines at the end of the buffer are not visible on screen", ->
+    describe "when some lines at the end of the buffer are not visible on screen", ->
       beforeEach ->
         editor.attachToDom(heightInLines: 5.5)
 
@@ -405,13 +405,13 @@ describe "Editor", ->
         editor.scroller.scrollTop(editor.lineHeight * 2.5)
         editor.scroller.trigger 'scroll'
 
-        expect(editor.lines.find('.line').length).toBe 6
-        expect(editor.lines.find('.line:first')).toHaveText buffer.lineForRow(2)
-        expect(editor.lines.find('.line:last')).toHaveText buffer.lineForRow(7)
+        expect(editor.lines.find('.line').length).toBe 8
+        expect(editor.lines.find('.line:first').text()).toBe buffer.lineForRow(0)
+        expect(editor.lines.find('.line:last').text()).toBe buffer.lineForRow(7)
 
         for line, index in editor.lines.find('.line')
           marginBottom = $(line).css('margin-bottom')
-          if index == 5
+          if index == 7
             expectedMarginBottom = (buffer.numLines() - 8) * editor.lineHeight
             expect(marginBottom).toBe "#{expectedMarginBottom}px"
           else

src/app/editor.coffee

@@ -237,34 +237,26 @@ class Editor extends View
     @lineCache = []
     @lines.find('.line').remove()
 
-    lastVisibleRow = @getLastVisibleRow()
-    @firstRenderedScreenRow = 0
-    @lastRenderedScreenRow = lastVisibleRow
+    lastVisibleScreenRow = @getLastVisibleScreenRow()
 
-    lineElements = @buildLineElements(0, lastVisibleRow)
-    lineElements.last().css('margin-bottom', (@getLastScreenRow() - lastVisibleRow) * @lineHeight)
+    lineElements = @buildLineElements(0, lastVisibleScreenRow)
+    lineElements.last().css('margin-bottom', (@getLastScreenRow() - lastVisibleScreenRow) * @lineHeight)
     @insertLineElements(0, lineElements)
 
   updateLines: ->
-    firstVisibleRow = @getFirstVisibleRow()
-    lastVisibleRow = @getLastVisibleRow()
+    lastVisibleScreenRow = @getLastVisibleScreenRow()
+    highestRenderedScreenRow = @lines.find('.line').length - 1
 
-    # if @firstRenderedScreenRow < firstVisibleRow
-    #   @lines.find('.line:first').remove() for row in [@firstRenderedScreenRow...firstVisibleRow]
-    #   @firstRenderedScreenRow = firstVisibleRow
-
-    if @lastRenderedScreenRow < lastVisibleRow
+    if lastVisibleScreenRow > highestRenderedScreenRow
       @lines.find('.line:last').css('margin-bottom', 'inherit')
-      console.log "building line elements for", @lastRenderedScreenRow + 1, lastVisibleRow
-      lineElements = @buildLineElements(@lastRenderedScreenRow + 1, lastVisibleRow)
-      lineElements.last().css('margin-bottom', (@getLastScreenRow() - lastVisibleRow) * @lineHeight)
-      @insertLineElements(@lastRenderedScreenRow + 1, lineElements)
-      @lastRenderedScreenRow = lastVisibleRow
+      lineElements = @buildLineElements(highestRenderedScreenRow + 1, lastVisibleScreenRow)
+      lineElements.last().css('margin-bottom', (@getLastScreenRow() - lastVisibleScreenRow) * @lineHeight)
+      @insertLineElements(highestRenderedScreenRow + 1, lineElements)
 
-  getFirstVisibleRow: ->
+  getFirstVisibleScreenRow: ->
     Math.floor(@scroller.scrollTop() / @lineHeight)
 
-  getLastVisibleRow: ->
+  getLastVisibleScreenRow: ->
     Math.ceil((@scroller.scrollTop() + @scroller.height()) / @lineHeight) - 1
 
   getScreenLines: ->
@@ -375,7 +367,6 @@ class Editor extends View
     @spliceLineElements(startRow, endRow - startRow + 1, lineElements)
 
   spliceLineElements: (startRow, rowCount, lineElements) ->
-    console.log "splice", startRow, rowCount, lineElements.length
     endRow = startRow + rowCount
     elementToInsertBefore = @lineCache[startRow]
     elementsToReplace = @lineCache[startRow...endRow]
@@ -388,7 +379,6 @@ class Editor extends View
       if elementToInsertBefore
         lines.insertBefore(fragment, elementToInsertBefore)
       else
-        console.log "appending child at start row", startRow, lineElements.text()
         lines.appendChild(fragment)
 
     elementsToReplace.forEach (element) =>