Switch out arbitrary segments of text in JavaScript

Question

Switch out arbitrary segments of text in JavaScript

I am attempting to replace a randomly selected substring within a string with another substring. Below is the code I am using:

function replaceRandomSubstring(str, substr, repl) {
  var amount = str.match(substr);
  var newstr = str;
  if (amount.length != -1) {
    var index = Math.floor(Math.random() * amount.length);
    var i = 0;
    do {
      if (i == index) newstr = newstr.replace(substr, repl);
      else newstr = newstr.replace(substr, "placeholder");
      i++;
    }
    while (i < index);
    newstr = newstr.split("placeholder").join(substr);
  }
  return newstr;
}

The issue I'm facing is that it only replaces the very first occurrence of the substring, not a random one as intended.

javascript replace substring

Answer 1

Answer №1

The reason for this behavior is that the amount function does not return all occurrences of the substrings in a string. It only returns the first match found.

An alternative solution is to utilize the String.prototype.matchAll() method:

function replaceRandomSubstring(str, substr, repl) {
  const amount = [...str.matchAll(substr)]; // gathering all substring matches in an array

  if (amount.length !== -1) {
    const index = Math.floor(Math.random() * amount.length);

    let i = 0;

    do {
      if (i === index) str = str.replace(substr, repl);
      else str = str.replace(substr, 'placeholder');
      i++;
    } while (i <= index);

    str = str.split('placeholder').join(substr);
  }
  return str;
}

Answer 2

The reason for this behavior is that the amount function does not return all occurrences of the substrings in a string. It only returns the first match found.

An alternative solution is to utilize the String.prototype.matchAll() method:

function replaceRandomSubstring(str, substr, repl) {
  const amount = [...str.matchAll(substr)]; // gathering all substring matches in an array

  if (amount.length !== -1) {
    const index = Math.floor(Math.random() * amount.length);

    let i = 0;

    do {
      if (i === index) str = str.replace(substr, repl);
      else str = str.replace(substr, 'placeholder');
      i++;
    } while (i <= index);

    str = str.split('placeholder').join(substr);
  }
  return str;
}

Switch out arbitrary segments of text in JavaScript

Answer №1

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