javascript：regexp以匹配未包含在自定义标签中的单词

Question

I need to match and replace all occurrences of 'word' that are not enclosed within the tags :$ and $: in a string. There may be other characters within the tags beside 'word'.

So, say I have the string

abc word hey :$ my word $:

And I need to replace word with letter ; Essentially I want to obtain the following string:

abc letter hey :$ my word $:

What is the best way to achieve that in JavaScript?

Further information:

tags won't be nested. the string may contain the characters ':' and '$' singularly. In this case they should be treated as simple characters and not as a tag.

Answer 1

I wasn't able to specify a RegExp for that, so here is a more imperative approach that does this - http://jsfiddle.net/dNhLm/

var text = "abc word hey :$ my word $:";
var replace = function(text, pattern, replacement) {
  var parts = [];
  // This will split the string into parts. The ones that has :$ we will have to proceed further and ignore
  var splitByEnd = text.split('$:');    
  for (i = 0, l = splitByEnd.length; i < l; i++) {
      // Here we should have at most 2 parts. The left one will be outside of the :$,$: pairs and is the
      // one we will apply the replacement. The right one if present will be between the :$,$: pairs and is
      // not a subject of replacement.
      var splitByStart = splitByEnd[i].split(':$');
      splitByStart[0] = splitByStart[0].replace(pattern, replacement);

      parts.push(splitByStart.join(':$'));
  }

  return parts.join('$:');
}

alert(replace(text, 'word', 'letter'));

Answer 2

I'm not sure regex is the right tool for the job here (a parser is likely more appropriate), but I guess one simple solution would be to cut out the bits covered by the tags, replacing all words, then replacing the tags. Something along the lines of this (which won't support nested tags, but should otherwise work):

var line = 'abc word hey :$ my word $: word :$ my word $:';
var tags = [];
var index = 0;
while (line.match(/:\$.*\$:/)) {
    var start = line.indexOf(':$');
    var end = line.indexOf('$:', start);
    var tag = line.substring(start, end + 2);
    line = line.replace(tag, '$tag' + index + '$');
    tags.push(tag);
    index++;
}
line = line.replace(/word/g, 'letter');
for (var i = 0; i < tags.length; i++) {
    line = line.replace('$tag' + i + '$', tags[i]);
}
document.write('result ' + line)

This outputs:

result abc letter hey :$ my word $: letter :$ my word $:

Answer 3

^(.+?)?(:\$.+?\$:)(.+?)?$

This will give you three capturing groups:

1. Everything before :? and ?:
2. The content inbetween your custom tags
3. Everything after :? and ?:

You then want to do an usual stringreplace on the first and third capturing group, replacing word with letter .

The first and third group are optional, to :?word?: another word will match, too.

var regex = /^(.+?)?(:\$.+?\$:)(.+?)?$/i;
regex.exec('abc word hey :$ my word $:');  
alert(RegExp.$1.replace("word", "letter") + RegExp.$2 + RegExp.$3.replace("word", "letter"));

Fiddle
Demo@debuggex

Answer 4

There's no easy regular expression, I can think of.

You can look for multiple regular expressions instead

var s1 = 'abc word hey :$ my word $: def word :$ another word $: word ghi :$ a third word $: jkl word';
var s2;

// word at the beginning
s2 = s1.replace(/^([^:$]*)word/, '$1letter');
// word at the end
s2 = s1.replace(/word([^:$]*)$/, 'letter$1');
// and word in between
s2 = s1.replace(/(:[^$]*)word([^$]*:)/g, '$1letter$2');
console.log(s2);

See JSFiddle