Wednesday, March 2, 2022

Optional object property with spread operator

I saw cool magic in my previous project. The optional object property.

Let see example:

Tuesday, February 22, 2022

Format Dates In JavaScript

Working with a date and time in JS was awful in the past. I dont know about you, but I used MomentJS or date-nfs library. 

Now it is possible to start using the Internationalization API for formating a date and time. Support is good in all browsers.

Let see an example:

If you want to use the browser’s locale, you must pass an empty Array in the constructor. The second argument is options. For more details see the documentation.

There is a Intl.RelativeTimeFormat() class for relative manipulation with a date and time. The Intl.RelativeTimeFormat is similar to the Intl.DateTimeFormat.

Let see an example:



Bonus :)

Friday, February 18, 2022

Streams - Transform

Transform streams are a special kind of Duplex stream. Transform streams apply some kind of transformation to each chunk of data that they receive from the Writable side, and then make the transformed data available on the Readable side.

For implementing a new Transform stream, we have to fill _transform() and optionally _flush() methods.

Let see example:

Thursday, February 17, 2022

Streams - Readable, Writable

Streams are one of the most important components of Node.js 

For example, the fs module has createReadStream() for reading from a file and createWriteStream() for writing to a file, the HTTP request and response objects are essentially streams, the zlib module allows compress and decompress data using a streaming interface and, crypto module exposes streaming primitives like createCipheriv and createDecipheriv.

Every stream in Node.js is an implementation of one of the four base abstract classes. Writable, Readable, Duplex, Transform. Each stream class is also an instance of EventEmitter.

Streams support two operating modes:

  • Binary mode - buffers or strings
  • Object mode: objects

Readable streams

A Readable stream represents a source of data. There are two approaches to receive the data from a Readable stream: non-flowing (or paused) and flowing. 

Paused mode

In paused mode, you need to call read() on the stream instance repeatedly until every chunk of data has been read.

The highWaterMark property, passed as an option to fs.createReadStream, determines how much data buffers inside the stream.

All Readable streams begin in paused mode but can be switched to flowing mode in one of the following ways: 

  • Adding a 'data' event handler.
  • Calling the stream.resume() method.
  • Calling the stream.pipe() method to send the data to a Writable.


Flowing mode

You can call readable.pause() and readable.resume()

Readable streams from iterables

You can create Readable stream instances from arrays or other iterable objects using the Readable.from()


Writable streams

A Writable stream represents a data destination. The example bellow shows an elegant way to create a gziped copy of a file.

In the next post, I am going to look at Transform streams.

Monday, February 14, 2022

Compare locale string

Hi guys

this is a simple post, but I feel it useful. 

I wrote a comparison function for the Czech language in many times. A friend of mine show me a Intl.Collator object today. I acknowledge that I have overlooked it in the past many times.

Lets look at example:


Functions chaining with reduce

Functions chain is very strong pattern in functional programing.

Let see a very simple example:

The evaluation of a functions chain takes place from right to left.

The last step is to create a universal chain function with any number of arguments. I use the reduceRight function from the array with this.

Happy coding.

Monday, January 31, 2022

Promises chaining with reduce

Hi devs,

I am going to made a promises chain with reduce function in this post. I think it is an elegant solution to the sequential execution of async tasks.

"Each .then() returns a newly generated promise object, which can optionally be used for chaining."
MDN Web Docs

Let's see example:



Now let's make chaining with reduce:

Friday, January 28, 2022

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.

Wednesday, January 26, 2022

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: 


Tuesday, January 25, 2022

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!

Thursday, January 13, 2022

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.

Friday, January 7, 2022

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: