no-cond-assign and while loops

I tried looking for some explanation but failed. What is an actual reasoning behind changing the default of this rule from except-parens to always?

The most typical example is looping over multiple matches of a single regexp.

var myRe = /ab*/g;
var str = 'abbcdefabh';
var myArray;
while ((myArray = myRe.exec(str)) !== null) {
  var msg = 'Found ' + myArray[0] + '. ';
  msg += 'Next match starts at ' + myRe.lastIndex;
  console.log(msg);
}

Is there a recommendation how to write this differently without breaking that rule setting? I tried do...while but there that’s either weird while(true) or a duplicate condition which feels rather weird.

do {
  var myArray = myRe.exec(str)
  if (myArray === null) break;
  var msg = 'Found ' + myArray[0] + '. ';
  msg += 'Next match starts at ' + myRe.lastIndex;
  console.log(msg);
} while(true) // or while(myArray !== null)

[ljharb]

In this specific situation - where there’s a gap in the language, and an active proposal to fix it (one I’m personally championing) - I’d recommend writing your own matchAll abstraction that overrides whatever eslint rules you need to, so that your real code doesn’t have to.

In general, conflating statements (assignment) with expressions (a conditional evaluation) is a really bad idea for code clarity. Also, the return value of a = b is not intuitive, and it’s really difficult to determine if you meant to do a == b or a === b - a = b in expression position looks like a bug.

[danielkcz]

Ok thank you for the explanation. I’ll probably just go with this for now which is much more readable and later I can replace it with real matchAll.

function matchAll(regex, text) {
  const matches = []
  let match = null
  // eslint-disable-next-line no-cond-assign
  while ((match = regex.exec(text)) !== null) {
    matches.push(match)
  }
  return matches
}