Typescript Case Study

Please send us your solution as a zip file or a link to a public git repository. It should contain a succinct report explaining your solution and thought process.

Exercise 1

Bootstrap a bun project using:

bun init -y

Create a function called fetchBalance.

async function fetchBalance(address: `0x${string}`): Promise<bigint>;

This function should fetch the balance of an Ethereum address and return a promise that resolves to the balance of the address in wei (bigint). You are not allowed to use any other library than the native Bun APIs.

You can use this Infura RPC endpoint: https://mainnet.infura.io/v3/f1b70935143f4b22b3c165d6bdfd3021

Your function should be able to batch requests and return the balance of multiple addresses in a single HTTP request.

For example this code should only do a single HTTP request:

const addresses = [
  "0xF7B31119c2682c88d88D455dBb9d5932c65Cf1bE",
  "0x3CBdeD43EFdAf0FC77b9C55F6fC9988fCC9b757d",
  "0x53b6936513e738f44FB50d2b9476730C0Ab3Bfc1",
  "0x72a5843cc08275C8171E582972Aa4fDa8C397B2A",
  "0x1da5821544e25c636c1417Ba96Ade4Cf6D2f9B5A",
] as const;

const balances = await Promise.all(addresses.map(fetchBalance));

and this example should only send 3 HTTP requests:

const addresses = [
  "0xF7B31119c2682c88d88D455dBb9d5932c65Cf1bE",
  "0x3CBdeD43EFdAf0FC77b9C55F6fC9988fCC9b757d",
  "0x53b6936513e738f44FB50d2b9476730C0Ab3Bfc1",
  "0x72a5843cc08275C8171E582972Aa4fDa8C397B2A",
  "0x1da5821544e25c636c1417Ba96Ade4Cf6D2f9B5A",
] as const;

const balances = await Promise.all(addresses.map(fetchBalance));

const balances_2 = await Promise.all(addresses.map(fetchBalance));

const balances_3 = await Promise.all([...addresses.map(fetchBalance), ...addresses.map(fetchBalance)]);

Exercise 2

Provide a better and safer implementation of the following typescript native types:

Example with toLowerCase:

const str = "HELLO";
const lowercase = str.toLowerCase(); // type of lowercase should be "hello" instead of string

interface String {
  
  /**
   * Returns string lowercased
   */
  toLowerCase(): string;
  /**
   * Returns true if searchString appears as a substring of the result of converting this
   * object to a String, at one or more positions that are
   * greater than or equal to position; otherwise, returns false.
   */
  includes(searchString: string, position?: number): boolean;

  /**
   * Split a string into substrings using the specified separator and return them as an array.
   */
  split(separator: string): string[];

  /**
   * Replaces text in a string, using a regular expression or search string.
   */
  replace(searchValue: string, replaceValue: string): string;

  /**
   * Returns true if the sequence of elements of searchString converted to a String is the
   * same as the corresponding elements of this object (converted to a String) starting at
   * position. Otherwise returns false.
   */
  startsWith(searchString: string, position?: number): boolean;
}