Type-safe URL Template

type_safe_url_template.ts

class PathTemplate<N extends string> {
  constructor(public fragments: string[], public paramNames: N[]) {}

  render(params: {[_ in N]: string}) {
    const buf = [this.fragments[0]];
    for (let i = 0; i < this.paramNames.length; ++i) {
      buf.push(params[this.paramNames[i]]);
      buf.push(this.fragments[i + 1]);
    }
    return buf.join('');
  }
}

function path<N extends string>(strs: TemplateStringsArray, ...ns: N[]): PathTemplate<N> {
  return new PathTemplate<N>([...strs], ns);
}

const template = path`/users/${'user_id'}/articles/${'article_id'}/comments/${'id'}`;
console.log(template.render({
  user_id: '1',
  article_id: '2',
  id: '3',
}));