Event loop in asynchronous

The event loop in javascript handle what happens behind the scenes in js when you call callback functions, DOM events etc..

How asynchronous works

const second = () => {
    setTimeout( () => {
        console.log("The end");
    }, 2000 );
};

const first = () => {
    console.log("Hey there !");
    second();
    console.log("It's ok !");
};

first();

1. In the execution stack we add on top the first execution context we now execute the code inside of this function, the first line is called so in the console you should now have hey there display. Then we call the second function we now put on top of the execution stack the second function.
2. We call the setTimeout function so we now have on the top of the execution stack the setTimeout function, but as you can see this function has a callback function which means she will be run asynchronously after 2s because of the second argument 2000.
3. What happen now ? We don't execute the code directly when the function is called because she's need to run asynchronously so the function will be moved into the Web api environment, from now the function will be running in the background of our code and we can keep going executing the code so we can remove the setTimeout execution context and also the second execution context.
4. Back in our first execution context we can execute the last line of code and now our console should have hey there it's ok. Right now all our synchronous code was executed we can now be focus on our asynchronous code.
5. Let's say that 2s are passed so our setTimeout function can now be executed so she will be moved to the message queue environment.
6. This environment hold all the functions who's waiting to be push in the execution stack as soon as this one is empty, in our example our execution stack is empty and our message queue environment contains the setTimeout function so we can push this one in the execution stack.
7. Our execution stack is now on top setTimeout function so we can execute the code inside this one and our console should now displayed hey there it's ok the end.

Current errors

This is a list of the main errors that you can meet:

Note: I'm not a wizard there is maybe some issue that you notice above so fell free to open an issue in the github repo if you find a new error not mentioned above.