CoffeeScript - simple loop doesn't execute as I think it should

Question

I am too new at javascript .. and have a problem with a simple coffee-script.

Script monitors 2 fields on a form and updates a third if the either of them changes. There "n" rows of the same type in the form. here is the code

    line_pre = "#po_polines_attributes_"
    watched  = [ "_qty", "_unit_price"]
    UpdateTotal = (ln)  ->
        jQuery  ->
          e1 = line_pre + ln +  watched[0]·
          e2 = line_pre + ln +  watched[1]
          new_total = $(e1).val()*$(e2).val()
          res = line_pre + ln + "_total_price"
          $(res).val(new_total)
     #   
     for indx in [0, 1, 2]
        do  ->  
           for w_fld  in watched
              do ->
                jQuery ->
                   $(line_pre + indx + w_fld).focusout ->
                      UpdateTotal(indx)

Code runs but only updates the last row of the data when qty or u_p are changed. I can't figure out why.

Also .. can anyone suggest how to find # of elements containing a string in jQuery/coffee $("input[name~='search_str']").length() doesn't work .. it appears that the returned element doesn't have "length/size" function.

mu is too short · Accepted Answer · 2014-02-16 06:50:42Z

1

Your dos are missing something: the loop values as arguments.

The function wrapper that do provides in something like this:

for i in a
  do -> ...

doesn't do much since the do's function will still be sharing the same i variable just like this JavaScript does:

for(i = 0; i < a.length; ++i)
  (function() {
    ...
  })();

But, if the do function gets i as an argument:

for i in a
  do (i) -> ...

then everything changes and you start doing what do is intended to do:

for(i = 0; i < a.length; ++i)
  (function(i) {
    ...
  })(i);

Notice how this do (i) -> version forces i to be evaluated when calling the function so that you're no longer working with the shared i.

Applying this to your loops yields:

for indx in [0, 1, 2]
  do (indx) ->
    for w_fld  in watched
      do (w_fld) ->
        jQuery ->
          $(line_pre + indx + w_fld).focusout ->
            UpdateTotal(indx)

answered Feb 16, 2014 at 6:50

mu is too short

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1 Comment

sms Over a year ago

Thanks for a quick response and full explanation -

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