JavaScript: "Dynamic" back reference RegExp replacement

Question

I want to make replacements like this:

var txt = "Some text containing $_variable1 and with $_variable2 inside of it as well.";
var rx = /(\$_[a-z]+)/g

var $_variable1 = "A CAT";
var $_variable2 = "A HOTDOG";

var replaced_txt = txt.replace(rx, $1);

I want replaced_txt to equal "...containing A CAT and with A HOTDOG ins...", but the only way to achieve this that I've found so far is this:

var replaced_txt = txt.replace(rx, function($1){return eval($1)});

And I have a feeling this is not the most elegant solution, no?

Preferably I'd like to avoid eval()

I'm grateful for any ideas on this!

/C

Pointy · Accepted Answer · 2010-12-01 18:06:46Z

1

You can do this:

var values = {
  '$_variable1': 'A CAT',
  '$_variable2': 'A HOTDOG'
};
var replaced_txt = txt.replace(rx, function(_, varName) {
  return values[varName] ? values[varName] : '<unknown variable: ' + varName + '>';
});

edited Dec 1, 2010 at 18:06

answered Dec 1, 2010 at 17:34

Pointy

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2 Comments

Kobi Over a year ago

Seems right. I'm pretty sure values[var] || 'default' would be neater here, and var may not be the best variable name (does it work?)

Pointy Over a year ago

... and yes you could do the || thing but I was trying to be clear for pedagogical reasons.

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