diff --git a/lib/misc/cells.js b/lib/misc/cells.js
index af611973..fb1eb679 100644
--- a/lib/misc/cells.js
+++ b/lib/misc/cells.js
@@ -1,45 +1,48 @@
 'use babel'
-
-import { get as weaveGet,
-         moveNext as weaveMoveNext,
-         movePrev as weaveMovePrev } from './weave.js'
-
+import {
+  get as weaveGet,
+  moveNext as weaveMoveNext,
+  movePrev as weaveMovePrev,
+} from './weave.js'
 import { getLine } from './blocks.js'
 
-import { Point } from 'atom'
-
-export function getRange (ed) {
+/**
+ * @param {TextEditor} editor
+ * @returns {[Point, Point]}
+ */
+export function getRange(editor) {
   // Cell range is:
   //  Start of line below top delimiter (and/or start of top row of file) to
   //  End of line before end delimiter
-  var buffer = ed.getBuffer()
-  var start = buffer.getFirstPosition()
-  var end = buffer.getEndPosition()
-  var regexString = '^(' + atom.config.get('julia-client.uiOptions.cellDelimiter').join('|') + ')'
-  var regex = new RegExp(regexString)
-  var cursor = ed.getCursorBufferPosition()
+  const buffer = editor.getBuffer()
+  const start = buffer.getFirstPosition()
+  const end = buffer.getEndPosition()
+  const regexString =
+    '^(' +
+    atom.config.get('julia-client.uiOptions.cellDelimiter').join('|') +
+    ')'
+  const regex = new RegExp(regexString)
+  const cursor = editor.getCursorBufferPosition()
   cursor.column = Infinity // cursor on delimiter line means eval cell below
-
-
   let foundDelim = false
-  for (let i = cursor.row + 1; i <= ed.getLastBufferRow(); i++) {
-    let {line, scope} = getLine(ed, i)
-    foundDelim = regex.test(line) && scope.join('.').indexOf('comment.line') > -1
+  for (let i = cursor.row + 1, l = editor.getLastBufferRow(); i <= l; i++) {
+    const { line, scope } = getLine(editor, i)
+    foundDelim =
+      regex.test(line) && scope.join('.').indexOf('comment.line') > -1
     end.row = i
     if (foundDelim) break
   }
-
   if (foundDelim) {
     end.row -= 1
     if (end.row < 0) end.row = 0
     end.column = Infinity
   }
-
   foundDelim = false
   if (cursor.row > 0) {
     for (let i = end.row; i >= 0; i--) {
-      let {line, scope} = getLine(ed, i)
-      foundDelim = regex.test(line) && scope.join('.').indexOf('comment.line') > -1
+      const { line, scope } = getLine(editor, i)
+      foundDelim =
+        regex.test(line) && scope.join('.').indexOf('comment.line') > -1
       start.row = i
       if (foundDelim) {
         break
@@ -47,63 +50,98 @@ export function getRange (ed) {
     }
     start.column = 0
   }
-
   return [start, end]
 }
 
-export function get (ed) {
-  if (ed.getGrammar().scopeName.indexOf('source.julia') > -1) {
-    return jlGet(ed)
+/**
+ * @param {TextEditor} editor
+ */
+export function get(editor) {
+  if (editor.getGrammar().scopeName.indexOf('source.julia') > -1) {
+    return jlGet(editor)
   } else {
-    return weaveGet(ed)
+    return weaveGet(editor)
   }
 }
 
-function jlGet (ed) {
-  var range = getRange(ed)
-  var text = ed.getTextInBufferRange(range)
+/**
+ * @param {TextEditor} editor
+ */
+function jlGet(editor) {
+  const range = getRange(editor)
+  let text = editor.getTextInBufferRange(range)
   if (text.trim() === '') text = ' '
-  var res = {
-    range: [[range[0].row, range[0].column], [range[1].row, range[1].column]],
-    selection: ed.getSelections()[0],
+  const res = {
+    range: [
+      [range[0].row, range[0].column],
+      [range[1].row, range[1].column],
+    ],
+    selection: editor.getSelections()[0],
     line: range[0].row,
-    text: text
+    text: text,
   }
   return [res]
 }
 
-export function moveNext (ed) {
-  if (ed == null) {
-    ed = atom.workspace.getActiveTextEditor()
+/**
+ * @param {TextEditor | null | undefined} editor
+ */
+export function moveNext(editor) {
+  if (!editor) {
+    editor = atom.workspace.getActiveTextEditor()
   }
-  if (ed.getGrammar().scopeName.indexOf('source.julia') > -1) {
-    return jlMoveNext(ed)
+  // TODO: getActiveTextEditor may return undefined
+  if (editor) {
+    if (editor.getGrammar().scopeName.indexOf('source.julia') > -1) {
+      return jlMoveNext(editor)
+    } else {
+      return weaveMoveNext(editor)
+    }
   } else {
-    return weaveMoveNext(ed)
+    console.error('No editor is given')
   }
 }
 
-function jlMoveNext (ed) {
-  var range = getRange(ed)
-  var sel = ed.getSelections()[0]
-  var nextRow = range[1].row + 2 // 2 = 1 to get to delimiter line + 1 more to go past it
-  return sel.setBufferRange([[nextRow, 0], [nextRow, 0]])
+/**
+ * @param {TextEditor} editor
+ */
+function jlMoveNext(editor) {
+  const range = getRange(editor)
+  const sel = editor.getSelections()[0]
+  const nextRow = range[1].row + 2 // 2 = 1 to get to delimiter line + 1 more to go past it
+  return sel.setBufferRange([
+    [nextRow, 0],
+    [nextRow, 0],
+  ])
 }
 
-export function movePrev (ed) {
-  if (ed == null) {
-    ed = atom.workspace.getActiveTextEditor()
+/**
+ * @param {TextEditor | undefined | null} editor
+ */
+export function movePrev(editor) {
+  if (!editor) {
+    editor = atom.workspace.getActiveTextEditor()
   }
-  if (ed.getGrammar().scopeName.indexOf('source.weave') > -1) {
-    return weaveMovePrev(ed)
+  if (editor) {
+    if (editor.getGrammar().scopeName.indexOf('source.weave') > -1) {
+      return weaveMovePrev(editor)
+    } else {
+      return jlMovePrev(editor)
+    }
   } else {
-    return jlMovePrev(ed)
+    console.error('No editor is given')
   }
 }
 
-function jlMovePrev (ed) {
-  var range = getRange(ed)
-  var prevRow = range[0].row - 2 // 2 = 1 to get to delimiter line + 1 more to go past it
-  var sel = ed.getSelections()[0]
-  return sel.setBufferRange([[prevRow, 0], [prevRow, 0]])
+/**
+ * @param {TextEditor} editor
+ */
+function jlMovePrev(editor) {
+  const range = getRange(editor)
+  const prevRow = range[0].row - 2 // 2 = 1 to get to delimiter line + 1 more to go past it
+  const sel = editor.getSelections()[0]
+  return sel.setBufferRange([
+    [prevRow, 0],
+    [prevRow, 0],
+  ])
 }