what is the best way to scroll through a list of _.map and _.forEach in lodash? I do not need the return value but I only do something inside the loop.

In terms of performance, which is the difference between the two functions?

a = []
b = []
list = response._source.carico_scarico
if angular.isDefined(list)
  _.forEach(list, (cs) ->
    if cs.qta >= 0 then a.push cs
    if cs.qta < 0 then b.push cs
  )

Or

a = []
b = []
list = response._source.carico_scarico
if angular.isDefined(list)
  _.map(list, (cs) ->
    if cs.qta >= 0 then a.push cs
    if cs.qta < 0 then b.push cs
  )

what is the best way to scroll through a list of _.map and _.forEach in lodash? I do not need the return value but I only do something inside the loop.

In terms of performance, which is the difference between the two functions?

a = []
b = []
list = response._source.carico_scarico
if angular.isDefined(list)
  _.forEach(list, (cs) ->
    if cs.qta >= 0 then a.push cs
    if cs.qta < 0 then b.push cs
  )

Or

a = []
b = []
list = response._source.carico_scarico
if angular.isDefined(list)
  _.map(list, (cs) ->
    if cs.qta >= 0 then a.push cs
    if cs.qta < 0 then b.push cs
  )

• javascript
• angularjs
• coffeescript
• lodash

• 3 you should do your own performance calculations. – Daniel A. White Commented Apr 27, 2015 at 12:48
• 1 "In terms of performance" - you need to objectively measure this yourself – James Thorpe Commented Apr 27, 2015 at 12:48
• So there is no way to know absolutely if one method is better than the other? – YoBre Commented Apr 27, 2015 at 12:58
• 2 There's a way to know absolutely for a given use case: Measure it. – T.J. Crowder Commented Apr 27, 2015 at 12:59

1 Answer 1

In terms of performance, which is the difference between the two functions?

It's extremely unlikely to matter. If you're worried about it mattering, create a test that's representative of your real code and try it (perhaps on http://jsperf.). But unless you're dealing with hundreds of thousands of entries, or repeating your loop hundreds of thousands of times, the real-world impact of any difference between them is likely to be nothing. (Heck, with modern JavaScript engines, hundreds of thousands may not even be enough to see a difference you'd care about.)

But speculating: As map has to create and populate an array to use as a return value (which you're going to ignore), and forEach doesn't, it stands to reason that map will be very very slightly slower.

But: The bigger argument here is using the right tool for the job: If you don't need the return value, don't use map. Its purpose is to create a result by mapping values from the original object into a new one. You don't want that, so map is an odd choice, likely to trip up people doing maintenance on the code down-the-line.