Fastest method to replace all instances of a character in a string [duplicate]

Answer 1

var mystring = 'This is a string';
var newString = mystring.replace(/i/g, "a");

newString now is 'Thas as a strang'

Answer 2

I just coded a benchmark and tested the first 3 answers. It seems that for short strings (<500 characters)
the third most voted answer is faster than the second most voted one.

For long strings (add ".repeat(300)" to the test string) the faster is answer 1 followed by the second and the third.

Note:

The above is true for browsers using v8 engine (chrome/chromium etc).
With firefox (SpiderMonkey engine) the results are totally different
Check for yourselves!! Firefox with the third solution seems to be
more than 4.5 times faster than Chrome with the first solution... crazy :D

function log(data) {
  document.getElementById("log").textContent += data + "\n";
}

benchmark = (() => {

  time_function = function(ms, f, num) {
    var z;
    var t = new Date().getTime();
    for (z = 0;
      ((new Date().getTime() - t) < ms); z++) f(num);
    return (z / ms)
  } // returns how many times the function was run in "ms" milliseconds.


  function benchmark() {
    function compare(a, b) {
      if (a[1] > b[1]) {
        return -1;
      }
      if (a[1] < b[1]) {
        return 1;
      }
      return 0;
    }

    // functions

    function replace1(s) {
      s.replace(/foo/g, "bar")
    }

String.prototype.replaceAll2 = function(_f, _r){ 

  var o = this.toString();
  var r = '';
  var s = o;
  var b = 0;
  var e = -1;
//      if(_c){ _f = _f.toLowerCase(); s = o.toLowerCase(); }

  while((e=s.indexOf(_f)) > -1)
  {
    r += o.substring(b, b+e) + _r;
    s = s.substring(e+_f.length, s.length);
    b += e+_f.length;
  }

  // Add Leftover
  if(s.length>0){ r+=o.substring(o.length-s.length, o.length); }

  // Return New String
  return r;
};

String.prototype.replaceAll = function(str1, str2, ignore) {
      return this.replace(new RegExp(str1.replace(/([\/\,\!\\\^\$\{\}\[\]\(\)\.\*\+\?\|\<\>\-\&])/g, "\\$&"), (ignore ? "gi" : "g")), (typeof(str2) == "string") ? str2.replace(/\$/g, "$$$$") : str2);
    }

    function replace2(s) {
      s.replaceAll("foo", "bar")
    }

    function replace3(s) {
      s.split('foo').join('bar');
    }

    function replace4(s) {
      s.replaceAll2("foo", "bar")
    }


    funcs = [
      [replace1, 0],
      [replace2, 0],
      [replace3, 0],
      [replace4, 0]
    ];

    funcs.forEach((ff) => {
      console.log("Benchmarking: " + ff[0].name);
      ff[1] = time_function(2500, ff[0], "foOfoobarBaR barbarfoobarf00".repeat(10));
      console.log("Score: " + ff[1]);

    })
    return funcs.sort(compare);
  }

  return benchmark;
})()
log("Starting benchmark...\n");
res = benchmark();
console.log("Winner: " + res[0][0].name + " !!!");
count = 1;
res.forEach((r) => {
  log((count++) + ". " + r[0].name + " score: " + Math.floor(10000 * r[1] / res[0][1]) / 100 + ((count == 2) ? "% *winner*" : "% speed of winner.") + " (" + Math.round(r[1] * 100) / 100 + ")");
});
log("\nWinner code:\n");
log(res[0][0].toString());

<textarea rows="50" cols="80" style="font-size: 16; resize:none; border: none;" id="log"></textarea>

The test will run for 10s (+2s) as you click the button.

My results (on the same pc):

Chrome/Linux Ubuntu 64:
1. replace1 score: 100% *winner* (766.18)
2. replace4 score: 99.07% speed of winner. (759.11)
3. replace3 score: 68.36% speed of winner. (523.83)
4. replace2 score: 59.35% speed of winner. (454.78)

Firefox/Linux Ubuntu 64
1. replace3 score: 100% *winner* (3480.1)
2. replace1 score: 13.06% speed of winner. (454.83)
3. replace4 score: 9.4% speed of winner. (327.42)
4. replace2 score: 4.81% speed of winner. (167.46)

Nice mess uh?

Took the liberty of adding more test results

Chrome/Windows 10
1. replace1 score: 100% *winner* (742.49)
2. replace4 score: 85.58% speed of winner. (635.44)
3. replace2 score: 54.42% speed of winner. (404.08)
4. replace3 score: 50.06% speed of winner. (371.73)

Firefox/Windows 10
1. replace3 score: 100% *winner* (2645.18)
2. replace1 score: 30.77% speed of winner. (814.18)
3. replace4 score: 22.3% speed of winner. (589.97)
4. replace2 score: 12.51% speed of winner. (331.13)

Edge/Windows 10
1. replace1 score: 100% *winner* (1251.24)
2. replace2 score: 46.63% speed of winner. (583.47)
3. replace3 score: 44.42% speed of winner. (555.92)
4. replace4 score: 20% speed of winner. (250.28)

Chrome on Galaxy Note 4

1. replace4 score: 100% *winner* (99.82)
2. replace1 score: 91.04% speed of winner. (90.88)
3. replace3 score: 70.27% speed of winner. (70.15)
4. replace2 score: 38.25% speed of winner. (38.18)

Answer 3

Just thinking about it from a speed issue I believe the case sensitive example provided in the link above would be by far the fastest solution.

var token = "\r\n";
var newToken = " ";
var oldStr = "This is a test\r\nof the emergency broadcasting\r\nsystem.";
newStr = oldStr.split(token).join(newToken);

newStr would be "This is a test of the emergency broadcast system."

Answer 4

Also you can try:

string.split('foo').join('bar');

Answer 5

Try this replaceAll: http://dumpsite.com/forum/index.php?topic=4.msg8#msg8

String.prototype.replaceAll = function(str1, str2, ignore) 
{
    return this.replace(new RegExp(str1.replace(/([\/\,\!\\\^\$\{\}\[\]\(\)\.\*\+\?\|\<\>\-\&])/g,"\\$&"),(ignore?"gi":"g")),(typeof(str2)=="string")?str2.replace(/\$/g,"$$$$"):str2);
} 

It is very fast, and it will work for ALL these conditions that many others fail on:

"x".replaceAll("x", "xyz");
// xyz

"x".replaceAll("", "xyz");
// xyzxxyz

"aA".replaceAll("a", "b", true);
// bb

"Hello???".replaceAll("?", "!");
// Hello!!!

Let me know if you can break it, or you have something better, but make sure it can pass these 4 tests.

Answer 6

@Gumbo adding extra answer - user.email.replace(/foo/gi,"bar");

/foo/g - Refers to the all string to replace matching the case sensitive

/foo/gi - Refers to the without case sensitive and replace all For Eg: (Foo, foo, FoO, fOO)

DEMO