How do I swap substrings within a string?

Question

I am trying to swap all occurrences of a pair of substrings within a given string.

For example, I may want to replace all occurrences of "coffee" with "tea" and all occurrences of "tea" with "coffee".

This is the first thing I thought of:

var newString = oldString.replace(/coffee/g, "__").replace(/tea/g, "coffee").replace(/__/g, "tea");

It works most of the time, but if my input string contains the substring "__", it will not work properly.

I am looking for something that works regardless of what input I give it, so I thought some more and came up with this:

var pieces = oldString.split("coffee");
for (var i = 0; i < pieces.length; i++)
  pieces[i] = pieces[i].replace(/tea/g, "coffee");
var newString = pieces.join("tea");

It works fine but it is kind of ugly and verbose. I tried to come up with something more concise and I used the map function built into jQuery to come up with this:

var newString = $.map(oldString.split("coffee"), function(piece) {
  return piece.replace(/tea/g, "coffee");
}).join("tea");

That is better but I still have a feeling that there is some brilliantly simple method that is failing to come to my mind. Does anyone here know a simpler way?

Answer 1

What about

theString.replace(/(coffee|tea)/g, function($1) {
     return $1 === 'coffee' ? 'tea' : 'coffee';
});

(Personally I think it's a crime to swap coffee and tea, but that's your business)

Answer 2

You can use a function:

var str = "I like coffee more than I like tea";
var newStr = str.replace(/(coffee|tea)/g, function(x) {
   return x === "coffee" ? "tea" : "coffee";
});
alert(newStr); 

Running example