Javascript accessing the string variable as array

Question

I just tried this code in Chrome deveoper tools:

var str = "1111111";
str[0] = 2;
2
console.log(str[0]);
1

As you can see, the output was 1, where I expected 2. My conclusion is this is not meant to be working like that, so I ask how would I get this to work - how would I change the first 'item' of the varable str to 2?

JS Strings are immutable; http://stackoverflow.com/questions/51185/are-javascript-strings-immutable-do-i-need-a-string-builder-in-javascript , use an array or vanilla string operations `(str = "2" + str.substr ...)` — Alex K., Aug 29 '12 at 11:02
possible duplicate of [How do I replace a character at a particular index in Javascript?](http://stackoverflow.com/questions/1431094/how-do-i-replace-a-character-at-a-particular-index-in-javascript) — Shawn Chin, Aug 29 '12 at 11:03
You can access string characters like an array, but not change them. — Bergi, Aug 29 '12 at 11:08

score 3 · Accepted Answer · answered Aug 29 '12 at 11:03

That is because in JavaScript strings are immutable objects. You should use substr function:

String.prototype.replaceAt = function (index, char) {
  return this.substr(0, index) + char + this.substr(index + char.length);
};

var str = '11111';
console.log(str.replaceAt(0, '2'));

defuz · Answer 2 · 2012-08-29T11:04:51.540

From the rhino book:

In JavaScript, strings are immutable objects, which means that the characters within them may not be changed and that any operations on strings actually create new strings. Strings are assigned by reference, not by value. In general, when an object is assigned by reference, a change made to the object through one reference will be visible through all other references to the object. Because strings cannot be changed, however, you can have multiple references to a string object and not worry that the string value will change without your knowing it.

score 0 · Answer 3 · answered Aug 29 '12 at 11:05

0

Try this out

str.replace(str.charAt(0), "2")

answered Aug 29 '12 at 11:05

pkurek

606
4
13

it's don't work, because `str.replace(str.charAt(1), "2")` return `"2111111"`, instead `"1211111"` – defuz Aug 29 '12 at 11:06

score 0 · Answer 4 · answered Aug 29 '12 at 11:05

0

You need to split the string first.

So something like:

str = str.split('');

Then you can treat it as an array.

answered Aug 29 '12 at 11:05

Mattyod

1,349
1
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Javascript accessing the string variable as array

4 Answers4