modifying strings as arrays

Question

I cannot understand why my word[1] returns an a instead of an i, could you help me understanding it?

var word = 'tangle';
document.write(word[1]); //returns 'a'
word[1] = 'i';
document.write(word[1]); //returns 'a'

(truth is, I wanted to make this, is my method wrong?)

//convert the first letter of each word of the string in upper case
var string = 'the quick brown fox';
stringSpl = string.split(' ');
for (var j=0; j<stringSpl.length; j++){
  stringSpl[j][0] = stringSpl[j][0].toUpperCase(); //this line is the faulty one
}
document.write(stringSpl.join(' '));

Lightness Races in Orbit · Accepted Answer · 2015-12-06 18:40:16Z

2

Strings are immutable in Javascript.

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.

Source: David Flanagan, in his book "JavaScript, The Definitive Guide, 4th edition" (ISBN: 978-0613911887).

edited Dec 6, 2015 at 18:40

Lightness Races in Orbit

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answered Dec 6, 2015 at 18:34

Mr_Pouet

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2 Comments

Lightness Races in Orbit Over a year ago

Cite your sources. Who wrote this text?

Mr_Pouet Over a year ago

Edited answer with source.

ruakh · Accepted Answer · 2015-12-06 18:35:25Z

1

Strings in JavaScript are immutable; rather than modifying them, you have to create a modified copy.

Note that word[1] is just syntactic sugar for word.charAt(1); just as you wouldn't expect word.charAt(1) = ... to modify the character returned by word.charAt(1) (because it's not returned by reference), you can't expect word[1] = ... to do so, either.

For your example, you can write something like this:

var string = 'the quick brown fox';
var titleCasedString =
  string.replace(/(^| )( )/g, function ($0, $1, $2) {
    return $1 + $2.toUpperCase();
  });
document.write(titleCasedString); // writes 'The Quick Brown Fox'

(using the replace method of string objects).

answered Dec 6, 2015 at 18:35

ruakh

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Comments

Ben Aston · Accepted Answer · 2015-12-06 18:35:00Z

0

Strings are not Arrays, but you can use an indexer syntax (similar to that of Arrays) to get characters from them.

You cannot, however, set elements using the same syntax.

Use String.prototype.split to create an Array from a String.

answered Dec 6, 2015 at 18:35

Ben Aston

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