Javascript - Replace substring from string where the value is between specific characters

Question

So I have this string, that represents a math expression:

(timezone*timelapse)-time

Each word represents an id from an input field, and currently i was merely replacing each word with a prototype js expression to be evaled later:

$('timezone').value,

$('timelapse').value

The problem is the last id. By the time i reach it, my expression is currently like this:

($('timezone').value*$('timelapse').value)-time

So when I search for the word time to replace it with $('time').value it will affect the first two values and messing the final expression.

My question here is: How can I replace the correct word here?

Since this a math expression the word should probably be between any math symbols like this:

(+-/* **word** +-/*)

[empty space] **word** +-/*)

(*-/* **word** [empty space]

Or not?

Guffa · Accepted Answer · 2013-02-15 14:12:27Z

4

You can replace all with one replacement, then you don't have the double replacement problem:

exp = exp.replace(/([A-Za-z]+)/g, function(m){
  return "$('" + m + "').value";
});

If it's a straight replacement without any logic, you can also use the caught value in a replacement string, as Cerbrus suggested:

exp = exp.replace(/([A-Za-z]+)/g, "$('$1').value");

edited Feb 15, 2013 at 14:12

answered Feb 15, 2013 at 12:34

Guffa

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2 Comments

Cerbrus Over a year ago

Your Kung-Fu is stronger than mine. +1 ... Although your style is imperfect, it can be compacted like this: .replace(/([A-Za-z]+)/g, "$('$1').value"); :P

Guffa Over a year ago

@Cerbrus: Yes, you are right, I didn't think of that option. The callback version is useful if it needs any further expansion.

Cerbrus · Accepted Answer · 2013-02-15 12:28:07Z

1

Try this:

var newString = oldString.replace(/\btime\b/, "$('time').value")

\b is a word boundary, meaning the regex only matches time if it's a stand-alone word, not when it's directly followed or preceded by any word characters.

answered Feb 15, 2013 at 12:28

Cerbrus

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10 Comments

Maxrunner Over a year ago

Thanks, this seems to do the trick, but it goes for only the first ocurrence, how i make this for all ocurrences? \b is a word boundary so, \bword\b what does the other / characters do at the beginning and end?

Cerbrus Over a year ago

The / characters are regex delimiters. They simply mean start regex and end regex. Use /\btime\b/g to make the regex work on all occurrences. (So, add a g after the second /)

Maxrunner Over a year ago

nice. Also if the value time is a variable string how can i mix with the regex?this doesn't seem to be working: var test=/\+variable+\b/g

Cerbrus Over a year ago

In that case you'll have to use the RegExp constructor, instead of a literal. Replace: /\btime\b/g with new RegExp("/\b"+variable+"\b/", "g")

Maxrunner Over a year ago

Humm seems to be failing to find anything...strange

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