City Fetcher API Challenge

Prompt

In JavaScript, we have two existing APIs that provide state and city data. Your task is to implement a function that fetches and combines data from both APIs to return all cities in a given country.

Requirements

Implement a function getAllCities(country) that uses the provided APIs (getStates and getCities) to return a promise resolving to an array of all cities in the given country.

Available APIs

• getStates(country) → Promise<string[]> // Returns array of state codes
• getCities(state) → Promise<string[]> // Returns array of cities in state

Playground

async function getAllCities(country) {
  try {
    // 1. Get states first
    // 2. For each state, how will you get cities?
    // 3. How will you combine all the cities?
    // 4. Return the final result
  } catch (error) {
    // How will you handle errors?
  }
}

Solution

Code Explanation 💻

Fetch States

• Call getStates(country) and await its result
• Returns: ['CA', 'NY', 'WA']

Create Promises for Cities

• Map over states array to create an array of promises
• Each promise represents a call to getCities(state)
• Returns: [Promise(CA cities), Promise(NY cities), Promise(WA cities)]

Resolve All Promises

• Use Promise.all() to wait for all city requests to complete
• Returns nested array:

[
  ['LA', 'SF', 'SD'], // CA cities
  ['LA1', 'SF1', 'SD1'], // NY cities
  ['LA2', 'SF2', 'SD2'], // WA cities
];

Flatten Results

• Use flat() to combine all cities into a single array
• Final result: ['LA', 'SF', 'SD', 'LA1', 'SF1', 'SD1', 'LA2', 'SF2', 'SD2']

Concept Explanation 🧠

Async/Await

• Makes asynchronous code look synchronous
• Improves code readability
• Simplifies error handling with try/catch

Promise.all()

• Executes all city requests in parallel
• More efficient than sequential requests
• Returns array of results in same order as input

Error Handling

• try/catch block catches errors from both APIs
• Properly propagates errors up the chain

Array Methods

• map(): Transforms array of states into array of promises
• flat(): Combines nested arrays into single array