Capitalize words in string [duplicate]

Question

/**
 * Capitalizes first letters of words in string.
 * @param {string} str String to be modified
 * @param {boolean=false} lower Whether all other letters should be lowercased
 * @return {string}
 * @usage
 *   capitalize('fix this string');     // -> 'Fix This String'
 *   capitalize('javaSCrIPT');          // -> 'JavaSCrIPT'
 *   capitalize('javaSCrIPT', true);    // -> 'Javascript'
 */
const capitalize = (str, lower = false) =>
  (lower ? str.toLowerCase() : str).replace(/(?:^|\s|["'([{])+\S/g, match => match.toUpperCase());
;

---

• fixes Marco Demaio's solution where first letter with a space preceding is not capitalized.

capitalize(' javascript'); // -> ' Javascript'

• can handle national symbols and accented letters.

capitalize('бабушка курит трубку');  // -> 'Бабушка Курит Трубку'
capitalize('località àtilacol')      // -> 'Località Àtilacol'

• can handle quotes and braces.

capitalize(`"quotes" 'and' (braces) {braces} [braces]`);  // -> "Quotes" 'And' (Braces) {Braces} [Braces]

The shortest implementation for capitalizing words within a string is the following using ES6's arrow functions:

'your string'.replace(/\b\w/g, l => l.toUpperCase())
// => 'Your String'

ES5 compatible implementation:

'your string'.replace(/\b\w/g, function(l){ return l.toUpperCase() })
// => 'Your String'

The regex basically matches the first letter of each word within the given string and transforms only that letter to uppercase:

• \b matches a word boundary (the beginning or ending of word);
• \w matches the following meta-character [a-zA-Z0-9].

For non-ASCII characters refer to this solution instead

'ÿöur striñg'.replace(/(^|\s)\S/g, l => l.toUpperCase())

This regex matches the first letter and every non-whitespace letter preceded by whitespace within the given string and transforms only that letter to uppercase:

• \s matches a whitespace character
• \S matches a non-whitespace character
• (x|y) matches any of the specified alternatives

A non-capturing group could have been used here as follows /(?:^|\s)\S/g though the g flag within our regex wont capture sub-groups by design anyway.

Cheers!

function capitalize(s){
    return s.toLowerCase().replace( /\b./g, function(a){ return a.toUpperCase(); } );
};

capitalize('this IS THE wOrst string eVeR');

output: "This Is The Worst String Ever"

Update:

It appears this solution supersedes mine: https://stackoverflow.com/a/7592235/104380

The answer provided by vsync works as long as you don't have accented letters in the input string.

I don't know the reason, but apparently the \b in regexp matches also accented letters (tested on IE8 and Chrome), so a string like "località" would be wrongly capitalized converted into "LocalitÀ" (the à letter gets capitalized cause the regexp thinks it's a word boundary)

A more general function that works also with accented letters is this one:

String.prototype.toCapitalize = function()
{ 
   return this.toLowerCase().replace(/^.|\s\S/g, function(a) { return a.toUpperCase(); });
}

You can use it like this:

alert( "hello località".toCapitalize() );

A simple, straightforward (non-regex) solution:

const capitalizeFirstLetter = s => 
  s.split(' ').map(w => w.charAt(0).toUpperCase() + w.slice(1)).join(' ')

1. Break the string into words Array (by space delimiter)
2. Break each word to first character + rest of characters in the word
3. The first letter is transformed to uppercase, and the rest remains as-is
4. Joins back the Array into a string with spaces

Ivo's answer is good, but I prefer to not match on \w because there's no need to capitalize 0-9 and A-Z. We can ignore those and only match on a-z.

'your string'.replace(/\b[a-z]/g, match => match.toUpperCase())
// => 'Your String'

It's the same output, but I think clearer in terms of self-documenting code.