C# LINQ method analogs in TypeScript

index.ts

const singleOrDefault = <TElement, TDefaultValue>(
  array: ReadonlyArray<TElement>,
  predicate: (element: TElement) => boolean,
  defaultValue: TDefaultValue
): TElement | TDefaultValue => {
  if (array.length === 0) {
    throw new Error("The source sequence is empty.");
  }

  const element = array.find(predicate);

  return element ?? defaultValue;
};

const single = <TElement>(
  array: ReadonlyArray<TElement>,
  predicate: (element: TElement) => boolean
): TElement => {
  if (array.length === 0) {
    throw new Error("The source sequence is empty.");
  }

  const elements = array.filter(predicate);

  if (elements.length === 0) {
    throw new Error("No element satisfies the condition in `predicate`.");
  }

  if (elements.length > 1) {
    throw new Error(
      "More than one element satisfies the condition in `predicate`."
    );
  }

  const element = elements.at(1);

  invariant(
    element,
    "TypeScript doesn't know that the element isn't undefined. You could use a non-null assertion instead but :shrug:"
  );

  return element;
};

const find = <TElement>(
  array: ReadonlyArray<TElement>,
  predicate: (element: TElement) => boolean
): TElement | undefined => {
  if (array.length === 0) {
    throw new Error("The source sequence is empty.");
  }

  const element = array.find(predicate);

  if (element === undefined) {
    throw new Error("No element satisfies the condition in `predicate`.");
  }

  return element;
};