Changing string characters in an array - Javascript

Question

I am working through some problems on CoderByte. The goal of this function is to take a string and capitalize the first letter of each word. For example, 'hello world' to 'Hello World'. I can't figure out why this code gives me 'hello world' and not 'Hello World'. I know this line array[i][0] = array[i][0].toUpperCase(); is the problem, but don't understand why it isn't working. I came up with an alternative solution but I am wondering why this didn't work. Thanks so much for your help!

function LetterCapitalize(str) { 
    var array = str.split(' ');
    for (var i = 0; i < array.length; i++) {
        array[i][0] = array[i][0].toUpperCase();
    }
return array.join('');
} 

LetterCapitalize('hello world');

Somewhat of a duplicate question see http://stackoverflow.com/questions/4878756/javascript-how-to-capitalize-first-letter-of-each-word-like-a-2-word-city — Winter Faulk, Nov 27 '16 at 21:29
var upperCased = str.split(" ").map(function(item) {return item.charAt(0).toUpperCase() + item.substr(1)}).join(" ") — JazzCat, Nov 27 '16 at 21:29
Possible duplicate of [How do I make the first letter of a string uppercase in JavaScript?](http://stackoverflow.com/questions/1026069/how-do-i-make-the-first-letter-of-a-string-uppercase-in-javascript) — Sreekanth, Nov 27 '16 at 22:02

score 2 · Answer 1 · edited May 23 '17 at 11:53

The issue is that array[i] refers to a string. However, strings are immutable in JavaScript, so this operation fails: array[i][0] = array[i][0].toUpperCase(). You cannot set individual indices on a string.

To accomplish what you want, you will have to create a new string with the first letter capitalized. Here's one way to do it, borrowing from another SO post:

function capitalizeFirstLetter(str) {
    return str.charAt(0).toUpperCase() + str.slice(1);
}

function capitalizeAllWords(str) { 
    var words = str.split(' ');
    return words.map(capitalizeFirstLetter).join(' ');
} 

capitalizeAllWords('hello world');

Ah ok I didn't realize that. Thank you very much for your help — davysamp, Nov 28 '16 at 18:07

P.S. · Answer 2 · 2016-11-27T22:09:29.833

1

You can just use regular expressions for this case:

function LetterCapitalize(str) { 
  var regex = /(\b[a-z](?!\s))/g;
  str = str.replace(regex, function(x) {
      return x.toUpperCase();
  });

  console.log(str);
} 

LetterCapitalize('hello world');

edited Nov 27 '16 at 22:09

answered Nov 27 '16 at 21:55

P.S.

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TheGenie OfTruth · Answer 3 · 2016-11-27T23:37:58.220

An effective way to deal with this would be using the .map() function

function cap(string){
    return string.split(" ").map(function(word){
        return word.charAt(0).toUpperCase() + word.slice(1)
    }
}

And a step by step guide to the code:

.split(" ") makes an array by adding a new item every time there is a space

.map() takes a value, plugs it into a function, and modifies the result based on what the function returns.

.charAt(0) gets the first letter and .toUpperCase() capitalizes it

.slice(1) Gets every letter after the first letter.

Cheers, TheGenieOfTruth

(Done on mobile, so formatting is spotty and code is untested)

Alan · Answer 4 · 2016-11-28T10:28:24.473

You did not create a two-dimensional array. Can't use the [0] reference -- have to use substrings.

Note the difference between substr (where the second parameter is a length -- we want only 1 character), and substring (where the second parameter is the ending position - omitted here so goes to end of string).

function LetterCapitalize(str) { 
    var array = str.split(' ');
    for (var i = 0; i < array.length; i++) {
        var firstChar = array[i].substr(0,1).toUpperCase();
        if array[i].length == 1
            array[i]=firstChar;
        else
            array[i]=firstChar + array[i].substring(1);
     }
    return array.join(' ');
} 

LetterCapitalize('hello world');

Correct. However, better to also provide an example, as "have to use substrings" is a broad statement that the OP may not understand. — Josh Beam, Nov 27 '16 at 21:40

webketje · Answer 5 · 2016-11-27T23:04:24.180

0

A go at a functional approach:

var capitalize = function(str) {
  return str.split(/\s+/)
   .map(function(word) { 
      return word.charAt(0).toUpperCase() + word.slice(1);
    })
  .join(' ');
};

As a bonus this function also accounts for \n (newline) and \t (tab) characters as capital letter boundaries.

edited Nov 27 '16 at 23:04

answered Nov 27 '16 at 22:58

webketje

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score -1 · Answer 6 · answered Nov 27 '16 at 21:43

Try this:

function LetterCapitalize(str) { 
        var array = str.split(' ');
        for (var i = 0; i < array.length; i++) {

            array[i] = array[i][0].toUpperCase()+array[i].slice(1);

        }
    return array.join(' ');
    } 

LetterCapitalize('hello world');

Changing string characters in an array - Javascript

6 Answers6