Eager & lazy Promise

Promises are always eager to the execution process. It means that when a Promise is created, the callback is immediately executed. That is ok, but sometimes you need call Promise in specific time, for example after setting some resources. 

The sollution is to wrap a Promise in a function.

Lets look an example:

Happy codding.

Conccurency Task queue

Spawning parallel tasks without control can often lead to excessive load. For instance sending bulk emails or downloads a lot of files slightly exceeds server resource limit.

In this post I am going to make a parallel tasks queue with concurrency limit control. 

This queue extends EventEmitter. It is possible to receive errors and get a message after finish.

Let see a queue:

Let see a examle:

Happy coding.

Resource: 

• Source code on Github

Try/ Catch Wrapper

Hey Guys,

do you also have a lots of Try/ Catch in the code? Of course yes. In my previous project I saw interesting wrapper for that.

Let see it:

Happy codding!

Arguments in arrow function in JavaScript

Yes, that is true. You canot use the arguments object in arrow function. But if you want to access  the arguments object in an arrow function, you can use the rest parameters feature.

See the example bellow:

Happy coding.

Conditional async import in JavaScript

In this post I am going to talk about conditional import module in JavaScript ( ECMAScript modules ).

The import statemen in JavaScript is static and therefore has two limitation:

1. a module identifier cannot be constructed at runtime
2. have to be declared at the top level of file and therefore cannot be nested within control flow statement like if statement.

In case you need conditional import you can use async dynamic import. Async import can be performed at runtime using special import() function.

The module identifier can be any module identifier supported by static import.

Let see example:

This form also supports the await keyword:

Playing with async function

 Async/ await is cool feature in JavaScript. Much has been written about it. In this post I would like to show how to resolve more independent async functions calls.

Let's have a simple promise call. It takes 1 second.

Now we will call the function multiple times using await. It takes aproximately 10 seconds.

When our asynchronous function is independent, it is useful to use Promise.all() instead of await. It fulfilled all promises in time approximately 1 second.

Javascript closures and recursion

What is a closure?

A closure is a feature in JavaScript where an inner function has access to the outer (enclosing) function’s variables.

I think, that closures are very handy for recursive call.

What is a recursion?

Simply said, the process in which a function calls itself.

When you create a recursive function, keep in mind that there must be an escape from the recursive function, otherwise you will get into an infinite loop.

Below I created a function, which call yourself. Recursion can be very complex, but the principle is the same.

Try it yourself: