JavaScript: Have we always been able to index into a string like it's an array?

Question

I've always thought that if you want to access the nth character in a string called str, then you have to do something like str.charAt(n). Today I was making a little dummy test page and by mistake, I accessed it with str[n] and to my surprise, it returned me the nth character of the string. I threw up this little purpose built page to exhibit this unexpected (to me) behaviour:

<!doctype html>
<html>
<body>
    <script>
        var str = "ABCDEFGH";
        if (str[4] === str.charAt(4)) alert("strings can be indexed directly as if they're arrays");
        var str2 = new String("ABCDEFGH");
        if (str2[4] === str2.charAt(4)) alert("even if they're declared as object type String");
    </script>
</body>
</html>

It wasn't always like this, was it?

See also this question: http://stackoverflow.com/questions/5943726/string-charatx-or-stringx — The Nail, Feb 17 '13 at 12:27

score 4 · Answer 1 · answered Feb 17 '13 at 12:24

There are two ways to access an individual character in a string. The first is the charAt method:
return 'cat'.charAt(1); // returns "a"
The other way is to treat the string as an array-like object, where individual characters correspond to a numerical index:
return 'cat'[1]; // returns "a"
Array-like character access (the second way above) is not part of ECMAScript 3. It is a JavaScript and ECMAScript 5 feature.

https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/String

Good to know, and makes it therefore unusable. It's charAt all the way !! — Dee2000, Feb 17 '13 at 12:44

score 3 · Accepted Answer · edited Feb 17 '13 at 12:26

3

No, that was not always possible.

If you run your code in an old enough browser, IE 7 for example, it won't be able to access the string like that. On those older engines, you'd have to use .charAt(index) instead.

edited Feb 17 '13 at 12:26

T.J. Crowder

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answered Feb 17 '13 at 12:23

Guffa

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Good to know, and makes it therefore unusable. It's charAt all the way !! – Dee2000 Feb 17 '13 at 12:45

score 2 · Answer 3 · answered Feb 17 '13 at 12:27

2

As long as I can remember, but:

Array-like character access [...] is not part of ECMAScript 3. It is a JavaScript and ECMAScript 5 feature.

(...and not supported in all browsers) See here.

answered Feb 17 '13 at 12:27

marsze

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Good to know, and makes it therefore unusable. It's charAt all the way !! – Dee2000 Feb 17 '13 at 12:45

JavaScript: Have we always been able to index into a string like it's an array?

3 Answers3

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