String Programs

String programs teach Unicode-aware iteration, searching, cleaning input, and formatting. JavaScript string length counts UTF-16 code units rather than user-perceived characters; for simple ASCII exercises this distinction may not matter, but real multilingual text needs attention.

Trimming removes surrounding whitespace; the regular expression splits on one or more whitespace characters. Spreading a string iterates code points, which is more appropriate than indexing UTF-16 code units for many cases.

Reversing Unicode code points is still not guaranteed to reverse grapheme clusters correctly; combined accents and emoji sequences need segmentation.

This source was compiled using TypeScript 5.8.3 with strict checking, then executed with Node.js 22.16.0. Its stdout below is the actual captured output. The core logic is runnable without a framework or a remote API; integration-specific examples appear in a separate lab when needed.

TypeScript source

function wordCount(text: string): number {
  const trimmed = text.trim();
  return trimmed ? trimmed.split(/\s+/u).length : 0;
}
function reverseCodePoints(text: string): string { return [...text].reverse().join(""); }
console.log(wordCount(" TypeScript   makes sense "));
console.log(reverseCodePoints("code"));

Verified output

3
edoc

Compile: npx tsc --strict --target es2022 --module commonjs string-programs.ts; run: node string-programs.js. For examples importing node: modules, install @types/node as a development dependency; for browser or React projects use the separate lab setup.

Trimming removes surrounding whitespace; the regular expression splits on one or more whitespace characters. Spreading a string iterates code points, which is more appropriate than indexing UTF-16 code units for many cases.

Before editing the code, predict what the output will be for one changed input. Run it and compare your prediction with the actual result.

Reversing Unicode code points is still not guaranteed to reverse grapheme clusters correctly; combined accents and emoji sequences need segmentation.

Determine whether the issue belongs to the type system, a trust boundary, or actual runtime behavior before choosing a correction.

Count vowels case-insensitively and then try sentences with punctuation and multiple spaces.

Record expected success and failure outcomes, run the code, and compare the observed behavior. Keep the exercise compatible with strict type checking.

Trimming removes surrounding whitespace; the regular expression splits on one or more whitespace characters. Spreading a string iterates code points, which is more appropriate than indexing UTF-16 code units for many cases.

Apply the same reasoning to the practice task, then integrate it into a real app only when the runtime and dependency setup are ready.