String title case function for Deno

readme.md

title_case.ts

Usage example:

import { titleCase } from "https://gist.githubusercontent.com/crabmusket/cd10f732e847afd023a00f6a45bd0d72/raw/558463e1c2a5aa910915a21396b105cefd1254d9/title_case.ts";

console.log(titleCase("deno is AWESOME"));
console.log(titleCase("words-can contain_punctuation"));
console.log(titleCase("  spacing is     preserved"));

Prints:

Deno Is Awesome
Words-can Contain_punctuation
  Spacing Is     Preserved

Run tests:

$ deno https://gist.githubusercontent.com/crabmusket/cd10f732e847afd023a00f6a45bd0d72/raw/558463e1c2a5aa910915a21396b105cefd1254d9/title_case_test.ts
running 4 tests
OK     titleCaseWorksWithAscii (0.00ms)
OK     titleCaseWorksWithUnicode (0.00ms)
OK     titleCasePreservesSpaces (0.00ms)
OK     titleCaseTreatsPunctuationAsLetters (0.00ms)
OK     titleCaseWorksWithEmoji (0.00ms)

test result: OK. 5 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out (2.00ms)

title_case.ts

/**
 * Convert a string to title case, i.e. the initial letter of each word is capitalised
 * and all other letters lowercased. The only word boundary that counts is whitespace,
 * and whitespace is preserved as-is.
 */
export function titleCase(input: string): string {
  return input.replace(/([^\s])([^\s]*)/g, replaceWord);

  function replaceWord(match: string, initial: string, trailing: string): string {
    return initial.toUpperCase() + trailing.toLowerCase();
  }
}

title_case_test.ts

import { test, runTests } from "https://deno.land/std@v0.11.0/testing/mod.ts";
import { assertEquals } from "https://deno.land/std@v0.11.0/testing/asserts.ts";
import { titleCase } from "./title_case.ts";

test(function titleCaseWorksWithAscii() {
  assertEquals(titleCase("hello world"), "Hello World");
  assertEquals(titleCase("HELLO WORLD"), "Hello World");
  assertEquals(titleCase("HeLlO wOrLd"), "Hello World");
});

test(function titleCaseWorksWithUnicode() {
  assertEquals(titleCase("çoban ırmak"), "Çoban Irmak");
  assertEquals(titleCase("çobanIrmak"), "Çobanirmak"); // capital I becomes lowercase i, of course
});

test(function titleCasePreservesSpaces() {
  assertEquals(titleCase(""), "");
  assertEquals(titleCase("  "), "  ");
  assertEquals(titleCase(" hello World"), " Hello World");
  assertEquals(titleCase("  hello  world  "), "  Hello  World  ");
});

test(function titleCaseTreatsPunctuationAsLetters() {
  assertEquals(titleCase("hello.world"), "Hello.world");
  assertEquals(titleCase("HELLO:WORLD"), "Hello:world");
  assertEquals(titleCase("HeLlO_wOrLd"), "Hello_world");
});

test(function titleCaseWorksWithEmoji() {
  assertEquals(titleCase("👋 world"), "👋 World");
  assertEquals(titleCase("🤷‍♀ing emoji"), "🤷‍♀ing Emoji"); // emoji counts as first letter of word
});

if (import.meta.main) {
  runTests();
}