capitalize function

Upper-cases the first character of a string, even outside the basic Unicode plane.

import { capitalize } from 'utils';

Signature

export function capitalize(input: string): string

Parameters

Name	Description
input	The string.

Returns

The string with its first character in upper case.

Example

capitalize('hello world'); // 'Hello world'
capitalize('élan'); // 'Élan'

Tests

Line coverage: 100 %.

• ✅ capitalizes "hello world" as "Hello world"
• ✅ capitalizes "Hello" as "Hello"
• ✅ capitalizes "hELLO" as "HELLO"
• ✅ capitalizes "élan" as "Élan"
• ✅ capitalizes "1st" as "1st"
• ✅ capitalizes "" as ""
• ✅ capitalizes "𐐨x" as "𐐀x"

Source

src/string/capitalize.ts (on GitHub)

Used by

• camelCase: Converts a string to camelCase; acronyms are words (XMLHttpRequest → xmlHttpRequest).
• pascalCase: Converts a string to PascalCase: words joined, each capitalized, the rest in lower case.
• sentenceCase: Converts an identifier to a sentence, to turn a key into a label: the first word capitalized, the others in lower case, acronyms kept.
• titleCase: Converts a string to Title Case: words separated by spaces, each capitalized, acronyms kept.
• trainCase: Converts a string to Train-Case: capitalized words joined with -, as in HTTP header names.

Source code

/**
 * Upper-cases the first character of a string, even outside the basic Unicode plane.
 *
 * @param input - The string.
 * @returns The string with its first character in upper case.
 * @example
 * capitalize('hello world'); // 'Hello world'
 * capitalize('élan'); // 'Élan'
 */
export function capitalize(input: string): string {
  const first = input.codePointAt(0);
  if (first === undefined) {
    return input;
  }
  const firstCharacter = String.fromCodePoint(first);
  return firstCharacter.toUpperCase() + input.slice(firstCharacter.length);
}

Test file

import { capitalize } from './capitalize';

describe(capitalize, () => {
  it.for([
    ['hello world', 'Hello world'],
    ['Hello', 'Hello'],
    ['hELLO', 'HELLO'],
    ['élan', 'Élan'],
    ['1st', '1st'],
    ['', ''],
    ['\u{10428}x', '\u{10400}x'],
  ] as const)('capitalizes %j as %j', ([input, expected]) => {
    expect(capitalize(input)).toBe(expected);
  });
});

Keywords: capitalize, strings, function