TypeScript API Error Handling with custom class

TypeScript Error Handling : Exercise-6 with Solution

Write a TypeScript program that reads data from an external API. Create a custom error class, 'ApiError', to handle errors related to API requests. Use this custom error class to catch and display API error messages.

Sample Solution:

TypeScript Code:

// Custom error class for API errors
class ApiError extends Error {
  constructor(message: string) {
    this.name = 'ApiError';

// Function to simulate an API request (replace with actual API request)
function fetchExternalApiData(): Promise {
  return new Promise((resolve, reject) => {
    // Simulate an API error
    setTimeout(() => {
      reject(new ApiError('Failed to fetch data from the API.'));
    }, 1000);

// Function to fetch data from the API and handle errors
async function fetchDataFromApi(): Promise {
  try {
    const apiData = await fetchExternalApiData();
    console.log(`Data from API: ${apiData}`);
  } catch (error) {
    if (error instanceof ApiError) {
      console.error(`API Error: ${error.message}`);
    } else {
      console.error(`Unexpected Error: ${error.message}`);

// Execute the API request and handle errors


In the exercise above -

  • First, we define a custom error class called ApiError that extends the built-in Error class. It takes a custom error message as a parameter and sets the error name.
  • The "fetchExternalApiData()" function simulates an API request using a Promise and rejects it with an ApiError containing a custom error message to simulate an API error.
  • The "fetchDataFromApi() function fetches data from the API using await and handles errors using a try-catch block. If an ApiError is caught, it displays the custom API error message. Otherwise, it handles other unexpected errors.


Unexpected Error: Failed to fetch data from the API.

TypeScript Editor:

See the Pen TypeScript by w3resource (@w3resource) on CodePen.

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