Synchronous, Asynchronous, Callback Hell, and Promises in JavaScript

Synchronous
In JavaScript, "synchronous" refers to the execution model where code runs in a sequential, blocking manner. This means that each operation must complete its execution before the next operation can begin.

Example code

console.log(1)
console.log(2)
console.log(3)
output print:
1
2
3

Asynchronous

  Asynchronous programming in JavaScript allows operations to run independently without blocking the main execution thread.

Example

console.log(1)

setTimeout(()=>{
console.log(2)
},2000)//here 2000 is (after 2 seconds)
console.log(3)
output print:
1
3
2(after 2 seconds)

Callback hell

 Callback Hell Explained with a Real-Life Example Imagine you are building a software project. The process usually goes like this:

Analysis → Gather requirements

Plan → Create a roadmap

Design → Decide how it should look/work

Develop → Write the code

Tester → Test the application

Deployment → Release the app

Here Problem: Callback hell makes code messy, hard to debug, and less readable.

Example

setTimeout(() => {
            console.log("Analysis");
            setTimeout(() => {
                console.log("Planing");
                setTimeout(() => {
                    console.log("Design");
                    setTimeout(() => {
                        console.log("Developer");
                            setTimeout(() => {
                            console.log("Testing");
                            setTimeout(() => {
                                console.log("Deployement");

                            },1000);

                        }, 1000);
                    }, 1000);

                }, 1000);
            }, 1000);
        }, 1000);

Promises

  We use the Promise its help to the code readability is easy inside the function execution.