In the previous lessons, we explored different ways to write asynchronous code in JavaScript, such as: All these approaches help us deal with tasks that do not complete immediately, such as API calls, timers, or user interactions. However, an important question often remains unanswered: In what order are these asynchronous operations actually executed? More specifically:…

According to the definition, async is a keyword that allows an asynchronous function to be written in a way that looks synchronous. But let’s not focus on definitions too much.Instead, let’s understand what actually happens. When you place the async keyword before a function, JavaScript automatically makes that function return a promise. Even if you…

Revisiting the problem with Promise.race() Suppose Eugene answers in 1 second, but he doesn’t have a pen. John and Susie respond later, but they do have pens. Since Promise.race() reacts to the first settled promise, the final result becomes a rejection. Here’s how that situation looks in code: Output: Even though Susie could help, Promise.race()…

The Core Idea of Promise.race() Promise.race(): This means: Real-Life Example: Borrowing a Pen at School Let’s understand this with a simple real-world example. Imagine: Each one replies at a different speed. Their response times: Friend Response Time Has a Pen? John 3 seconds Yes Eugene 5 seconds No Susie 2 seconds Yes You don’t want…

In the previous lessons, we discussed Promise.all() and how it works when executing multiple asynchronous operations in parallel. You also saw an important limitation: If any one promise rejects, Promise.all() immediately rejects and stops waiting for the remaining promises. In this tutorial, we’ll explore a safer alternative — Promise.allSettled() This method allows you to run…

In many real-world applications, we often need to execute multiple asynchronous operations at the same time and wait for all of them to finish before proceeding. A very common example of this is when an application needs to make multiple HTTP requests in parallel — such as fetching data from different services — and only…

Understanding Promise.resolve() and Promise.reject() In this tutorial, we are going to understand two very important JavaScript methods that help us convert any value into a Promise: These methods are extremely useful when working with existing code that expects Promises, but sometimes you only have normal (non-promise) values. Why Do We Need This? In real-world JavaScript…

Using .then() with One or Two Arguments The .then() method can accept two arguments: So far, we mostly used .then() with only one argument, which handles successful cases. Example: Handling Both Success and Failure Let’s use our familiar calculateSquare function. This works correctly: However, this approach has a limitation. The Hidden Problem Let’s introduce an…

The Key Idea: .then() Returns a New Promise This is extremely important: Every .then() call returns a new promise. Because of this: This allows us to create a chain of asynchronous operations. Step 1: Basic Promise Chain Let’s start with a simple example. Output: So far, nothing new. Step 2: Adding Another .then() Now let’s…