gistfile1.txt

Something.prototype.aFunction = function() {
  var _this = this
  
  this.collection.forEach(_this.bFunction)
  this.collection.forEach(function(item) {
    _this.bFunction(item)
  })
}

Something.prototype.bFunction = function(item) {
  // invoked from line 4, this is 'Window'
  // invoked from line 6, this is 'Something'
  console.log(this)
}