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How do I string.format() or sprintf() in coffeescript?

This seems to do the trick:

String.prototype.format = ->
  args = arguments
  return this.replace /{(\d+)}/g, (match, number) ->
    return if typeof args[number] isnt 'undefined' then args[number] else match

Translated using this javascript from fearphage

Which can then be used like this:

fmt = "<p>{0} {1} (<a href='mailto:{2}'>{2}</a>)</p>"
mystring = fmt.format "Fred", "Flinstone", "[email protected]"

mystring would then be:

<p>Fred Flinstone (<a href='mailto:[email protected]'>[email protected]</a>)</p>

Using the #{var} approach (while perfect for example given) doesn't work with a string that needs to be recycled several times. In a looping situation for example.

  HTML_header       = fs.readFileSync('includes/notify/header.html').toString()
  HTML_managerOpen  = fs.readFileSync('includes/notify/managerOpen.html').toString()
  HTML_student      = fs.readFileSync('includes/notify/student.html').toString()
  HTML_managerClose = fs.readFileSync('includes/notify/managerClose.html').toString()
  HTML_footer       = fs.readFileSync('includes/notify/footer.html').toString()

HTML_final = HTML_header

   getter2 = (r, callback) ->
      HTML_final += HTML_managerOpen.format r.EMAIL, r.FNAME, r.LNAME, r.STUDENTS.length, r.PHONE, r.MEMAIL, r.MFNAME, r.MLNAME
      async.forEachSeries r.STUDENTS, getter3, (err) ->
        HTML_final += HTML_managerClose
        callback null

    getter3 = (r, callback) ->
      HTML_final += HTML_student.format r.EMAIL, r.FNAME, r.LNAME, r.PHONE, r.DESCRIPTION, r.ENROLLED, "", "", "", "", "", "", r.CERTEXAMSCORE, r.COIKEY
      callback null

async.forEachSeries results, getter2, (err) ->
  cback null, HTML_final + HTML_footer
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75% accept rate
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Is this a question? – David Ellis Mar 26 at 22:27
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1 Answer

up vote 2 down vote accepted

So there's 2 things going on here. First is interpolation, which coffeescript directly supports using double-quoted string literals and ruby style syntax like this:

"The #{speed} #{color} #{animal} jumped over the lazy dog"

That will replace the placeholders with the corresponding variables from the local scope. That's the idiomatic way to handle string interpolation in coffeescript (and ruby).

Second is the formatting, which you should probably handle separately if you want to get numbers with specific decimal places, thousands separate with commas, leading zeros, or that sort of thing. However, CoffeeScript can interpolate the formatting as well, so you could do

"Free shipping on orders over #{currency(freeShipAmount)}"
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Good point - Thanks for reminding me to explain why I was trying to find a string.format() solution instead of using "....#{var}...." – jiy Mar 26 at 23:03
Sounds like you problem is solved. Would you mind accepting my answer so I get those oh-so-yummy points and your accept rate goes up? – Peter Lyons Mar 27 at 18:56
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