prototype function prints itself instead of the result

Question

I was answering a question here Is there a JavaScript equivalent of rubys "#{}" sequences? when i run in a problem with javascript prototype. I wanted to provide an alternative way of the first working function which gives a ruby way of printing, formatting and concatenating strings. Why is the normal function working and the prototype function not ?

<script>
function p(str){
  document.write(str.replace(/#{(\w)}/g, function(match, s){return eval(s)})+"<br>");
}

String.prototype.p = function() {
  return this.replace(/#{(\w)}/g, function(match, s){return eval(s)})+"<br>";
};


var f="foo", b="bar"
p("#{f} #{b}")
document.write("#{f} #{b}".p);

</script>

this gives

foo bar
function () { return this.replace(/#{(\w)}/g, function(match, s){return eval(s)})+"
"; }

the first line is correct, it is the concatenated string, the second line is the function itself that is printed, not the result..

is there anyone who knows how to avoid the eval here ? – peter Apr 13 '12 at 21:04 — peter, Apr 13 '12 at 21:04

score 2 · Accepted Answer · answered Apr 13 '12 at 20:49

2

"#{f} #{b}".p refers to the function itself (String.p), because "#{f} #{b}" is a string.

You want "#{f} #{b}".p() for it to print foo bar.

answered Apr 13 '12 at 20:49

Heitor Chang

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of course ! stupid of me, i'm already too accustomed to ruby i guess, thanks – peter Apr 13 '12 at 20:54

prototype function prints itself instead of the result

1 Answers1