Splitting string into matching and non-matching groups in javascript

Question

I am trying to split the string into an array of strings those matching a regular expression and those that don't:

string = "Lazy {{some_animal}} jumps over.."
# do some magic with regex /({{\s?[\w]+\s?}})/g and its negation
array = ["Lazy ", "{{some_animal}}", " jumps over.."]

Best performant way to do that in javascript?

Answer 1

You can use String match for that

The regex below simply matches anything that's not a mustach, optionally surrounded by mustaches.

Example snippet:

var str = "Lazy {{some_animal}} jumps over..";

const pattern = /\{*[^{}]+\}*/g;

var array = str.match(pattern);

console.log(str);
console.log(pattern);
console.log(array);

But to make it more precise, the regex pattern becomes a bit more complicated.
The regex below matches:

1. "what you want"
   (a word between 2 mustaches on each side)
2. OR "what you don't want followed by what you want"
   (using lazy matching and positive lookahead)
3. OR "what remains"

var str = "Lazy {{some_animal}} jumps over..";

const pattern = /\{\{\w+\}\}|.+?(?=\{\{\w+\}\})|.+/g;

var array = str.match(pattern);

console.log(str);
console.log(pattern);
console.log(array);

And last but not least, the evil SM method.
Split AND Match on the same regex. And concatinate them into a single array.
The downside of this method is that the order is not preserved.

var str = "Lazy {{some_animal}} jumps over..";

const pattern = /\{\{\w+\}\}/g;

var what_you_want = str.match(pattern);
var what_you_dont_want = str.split(pattern);

var array = what_you_want.concat(what_you_dont_want);

console.log(str);
console.log(pattern);
console.log(array);

Answer 2

I'm fairly sure a simple exec loop is going to be your best option:

function getSegments(rex, str) {
  var segments = [];
  var lastIndex = 0;
  var match;
  rex.lastIndex = 0; // In case there's a dangling previous search
  while (match = rex.exec(str)) {
    if (match.index > lastIndex) {
      segments.push(str.substring(lastIndex, match.index));
    }
    segments.push(match[0]);
    lastIndex = match.index + match[0].length;
  }
  if (lastIndex < str.length) {
    segments.push(str.substring(lastIndex));
  }
  return segments;
}

var rex = /{{\s?[\w]+\s?}}/g;
var string = "Lazy {{some_animal}} jumps over..";

console.log(getSegments(/{{\s?[\w]+\s?}}/g, string));

Note I removed the capture group; it's not needed for this sort of solution.