fnbuilder.tsx

const context = ['sin', 'cos', 'exp']
  .map((name) => ('const ' + name + ' = Math.' + name + '; '))
  .join('');

export const buildFunction = (fn: string): (x: number) => number => {
  const fullFn = '(x) => { ' + context + ' return (' + fn + '); }';
  return eval(fullFn);
}