Changing string characters in an array - Javascript

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');

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');

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)

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.

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');

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');