Fix #4882: Range not declaring var for the "i" (#4883)

* fix #4882

* test

Author: zdenko

lib/coffeescript/nodes.js

@@ -1353,7 +1353,11 @@ exports.Range = class Range extends Base
     idx      = del o, 'index'
     idxName  = del o, 'name'
     namedIndex = idxName and idxName isnt idx
-    varPart  = "#{idx} = #{@fromC}"
+    varPart  =
+      if known and not namedIndex
+        "var #{idx} = #{@fromC}"
+      else
+        "#{idx} = #{@fromC}"
     varPart += ", #{@toC}" if @toC isnt @toVar
     varPart += ", #{@step}" if @step isnt @stepVar
     [lt, gt] = ["#{idx} <#{@equals}", "#{idx} >#{@equals}"]

src/nodes.coffee

@@ -195,3 +195,10 @@ test "#2047: from, to and step as variables", ->
   step = 0
   r = (x for x in [b..a] by step)
   arrayEq r, []
+
+test "#4884: Range not declaring var for the 'i'", ->
+  'use strict'
+  [0..21].forEach (idx) ->
+    idx + 1
+
+  eq global.i, undefined