Master Asynchronous JavaScript for Interview Success

Describe Promise.all, a static method that takes an iterable of promises and returns a single promise that fulfills when all resolve and yields results, or rejects on the first failure.

Test the promise.all behavior with three resolved promises, including a happy path and a rejection scenario using async/await, setTimeout delays, and mock API calls to ensure output order matches input.

Implement your own promise.all by building a function that accepts a list of promises, resolves to an array of results, and rejects on the first error.

Promise.allSettled processes an iterable of promises and returns a single promise that fulfills when all settle. It yields an array of outcomes with status, value, or reason, unlike Promise.all.

Learn how to implement and test promise.all settled, replacing promise.all, handling fulfilled and rejected results, extracting values, and validating statuses and outputs through unit tests.

Implement a custom promise.allSettled on the Promise class to return an array of objects with status and value, handling fulfilled and rejected cases alike, always delivering all results.

Promise.any is a static method taking an iterable of promises and returns the first fulfilled value. It rejects only when all promises reject, including an empty table, with aggregated results.

Learn how to write and refine unit tests for Promise.any in JavaScript. Verify first-resolve behavior, rejection handling, and cross-environment compatibility across Node versions.

Develop a custom Promise.any by returning the first fulfilled promise and, if all reject, an aggregate error with all rejection reasons, using a promise constructor and input normalization.

Promise.race takes an array of promises and returns a single promise that settles with the first promise to settle, fulfilled or rejected. Unlike Promise.any, it uses the first settled promise.

Write unit tests for promise.race to verify that the first settled promise (whether resolved or rejected) wins, including the fastest API call scenario and handling delays.

Implement your own promise race function that takes a list of promises and settles on the first to resolve or reject, returning a new promise.

Learn how to promisify a callback-based function into a promise-based one, enabling readable asynchronous code with resolve and reject, as shown with a read file example.

Write unit tests for a promisify function, validating resolve and reject paths with a callback-based original function and the utils.promisify helper.

Implement your own promisify by creating a function that accepts another function, returns a new function that returns a Promise, forwards arguments, and resolves or rejects via a callback.

Learn how throttle enforces a maximum number of function calls over time, such as once every 100 milliseconds, and how setTimeout helps prevent heavy API calls during scrolling.

Learn to unit test lodash throttle by importing the library, creating a spy function, and asserting calls occur only once within a 200-millisecond window, with adjusting timer intervals for reliability.

Develop and test your own throttle function in JavaScript by using setInterval and setTimeout to limit calls to once every 200 milliseconds, wiring through apply and closures to forward arguments.

Apply the debounce function in JavaScript to trigger a single action after the user stops typing. Use it for search suggestions and auto save, reducing API calls and boosting performance.

Create unit tests for a debounce function, validating a single call after the delay and correct parameter and context propagation. Verify behavior under rapid calls and timer cleanup.

Implement a custom debounce function in JavaScript that accepts a callback and delay. Return a function that preserves context and arguments, clears timeouts, and fires the callback after the delay.

Learn how the JavaScript async helper sequence function runs an array of asynchronous tasks in sequential order, passing results from one to the next until resolution or rejection.

Write unit tests for the async helper sequence function that resolves a list of asynchronous tasks sequentially and returns the final result, including rejection handling.

Master asynchronous JavaScript for interview success by learning the parallel function, an asynchronous helper that runs an array of promise-returning tasks in parallel, resolving all results or rejecting on error.

Test unit tests for a promise-based async helper parallel function that resolves an array of parallel functions, with and without callback, and handle rejection.

Implement a parallel function that runs a list of promises or promise-returning callbacks in parallel using Promise.all, resolves with mapped results, and rejects on any failure, with optional callback handling.