Modifying elements of a string directly

Question

I have a string. It's just like;

var str = "This is an example sentence, thanks.";

I want to change every fifth element of this string.

for(var i=5; i<=str.length; i=i+5)
{
   str[i]='X';  // it doesn't work, I need something like that
}

So I want str to be "ThisXis aX exaXple XenteXce, XhankX."

Is there any way to do that?

have you tried with [concat()](http://www.w3schools.com/jsref/jsref_concat_string.asp) and [substring()](http://www.w3schools.com/jsref/jsref_substring.asp)? — dani herrera, Dec 28 '11 at 20:54
Here is related discussion http://stackoverflow.com/questions/1431094/how-do-i-replace-a-character-at-a-particular-index-in-javascript — kosa, Dec 28 '11 at 21:01

score 3 · Accepted Answer · answered Dec 28 '11 at 20:59

3

Use RegEx

str = str.replace(/(....)./g, "$1X")

jsfiddle

answered Dec 28 '11 at 20:59

Shiplu Mokaddim

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John Hartsock · Answer 2 · 2011-12-28T21:01:13.993

2

var str = "This is an example sentence, thanks.";

var newString = "";
for(var i=0; i<str.length; i++)
{
   if ((i % 5) == 4) {
     newString += "X";
   } else {
     newString += str.charAt(i);
   }
}

Here is a running example. http://jsfiddle.net/WufuK/1

edited Dec 28 '11 at 21:01

answered Dec 28 '11 at 20:54

John Hartsock

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+1 but for IE 8 and lower, `str[i]` should be `str.charAt(i)`. – Dec 28 '11 at 21:00

Andreas Köberle · Answer 3 · 2011-12-28T21:38:53.737

2

You can use string.substring()

var a = "This is an example sentence, thanks.";
var result ="";
for(var i=0;i <a.length-1; i+=5){
    result +=a.substr(i, 4)+'X';
}

alert(result)

jsFiddle: http://jsfiddle.net/mVb4u/5

edited Dec 28 '11 at 21:38

answered Dec 28 '11 at 21:00

Andreas Köberle

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You may want to take another look at the result in your Fiddle. You should be doing `a.substr(i, 4)+'X'` or `a.substring(i, i+4)+'X'`. – Dec 28 '11 at 21:15

score 2 · Answer 4 · answered Dec 28 '11 at 21:03

2

You could use a map, although the regex solution looks better.

str = str.split('').map(function(chr, index){
  return (index % 5 === 4)? 'X' : chr;
}).join('');

answered Dec 28 '11 at 21:03

david

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Note that ie8 and lower doesn't support `map()`. – Andreas Köberle Dec 28 '11 at 21:10
ie doesn't support much of anything :( – david Dec 28 '11 at 21:25

kojiro · Answer 5 · 2011-12-28T22:21:04.440

2

This approach uses Array.reduce, which is native to JavaScript 1.8, but can be backported.

Array.prototype.reduce.call("This is an example sentence, thanks.", function(p,c,i,a) { return p + ( i % 5 == 4 ? "X" : c); });

Update: Updated to reflect am not i am's comments below.

edited Dec 28 '11 at 22:21

answered Dec 28 '11 at 21:05

kojiro

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You probably mean `Array.prototype.reduce.call("This is...)` – Dec 28 '11 at 21:08
@amnotiam no, I actually meant what I wrote. Your method would work in older versions of JavaScript, but [Array generics](https://developer.mozilla.org/en/New_in_JavaScript_1.6#Array_and_String_generics) are available in 1.6 and up. – kojiro Dec 28 '11 at 21:53
1

Well the link in your question links to the compatibility patch for `Array.prototype.reduce`, not `Array.reduce`. Would be a good idea to note that you're referring to that non-ES-standard Mozilla extension. The closest it is to standard right now seems to be [this strawman proposal](http://wiki.ecmascript.org/doku.php?id=strawman:array_statics). – Dec 28 '11 at 22:05
1

@amnotiam Good point, I was misled by the MDN. Normally when something is nonstandard they point it out. – kojiro Dec 28 '11 at 22:19

Modifying elements of a string directly

5 Answers5