DEV Community: Gajender Tyagi

Job Q V/S Callback Q

Gajender Tyagi — Wed, 06 Oct 2021 03:13:22 +0000

🥊 Who wins when we have tasks waiting to be implemented in Job queue as well as in Callback queue.

Hmmmm.... let's see who wins with the piece of code below. 🔈

// setTimeout is a web API which waits for the time as given // in 2nd parameter and then moves the callback function in 
// call back queue   
setTimeout(() => console.log('1'), 0);
setTimeout(() => console.log('2'), 10);

// Promise is a class in JavaScript so the functionality is 
// native, to handle the functions executed we have a Job 
// queue
Promise.resolve('hi').then((data) => console.log('3'))

console.log('4');

If you execute this code the logs will be

This proves that JobQ has priority over callback queue if call stack is empty, Of course!.

Thoughts in comments

🦕 ⌨️

Implicit Explicit and....?

Gajender Tyagi — Sat, 25 Sep 2021 07:26:28 +0000

Hello, today i was reading about this, you ask what I say this is a keyword in JavaScript which refers to ......?

Well this is a question we will try to answer today.

Code 1 - Implicit binding


this.name = 'Global Name';

const person = {
  name: 'James Bond',
  profession: 'Agent',
  id: '007'
  hi: function() { 
    return this.name   
  } 
} 

person.hi() // 'James Bond'

Well, clearly this refers to its immediate object.

Now lets change this a little bit


this.name = 'Global Name';

const person = {
  name: 'James Bond',
  profession: 'Agent',
  id: '007'
  hi: () => { 
    return this.name   
  } 
} 

person.hi() // 'Global Name'

If you see clearly I have changed hi key's value to an arrow function and arrow functions changes the reference this to global object. But why ? can you answer in comments ?

Code 2 - Explicit binding


this.name = 'Global Name';

const person = {
  name: 'James Bond',
  profession: 'Agent',
  id: '007'
  hi: function() { 
    return this.name   
  }.bind(window) 
} 

person.hi() // 'Global Name'

In here this will refer to global object since we have bind it to window object which is the global object.

Thank you

Compare objects in JS

Gajender Tyagi — Sun, 12 Sep 2021 08:38:31 +0000

How can you compare to objects with same properties cause we know both the objects all though same values but sits at different memory location hence they will be not equal.

var user1 = {name : "nerd", org: "dev"};
var user2 = {name : "nerd", org: "dev"};
var eq = user1 == user2;
alert(eq); // gives false

Taken from Andrei course for Advance Javascript

Well a simple solution could be this

var user1 = {name : "nerd", org: "dev"};
var user2 = {name : "nerd", org: "dev"};
var eq = JSON.stringify(user1) == JSON.stringify(user2);
alert(eq);

By converting the objects into sting the values can be compared but we have to be care full of the spaces and cases to be exact in both the objects.

A deep dive discussion for the same can be found on the stackoverflow page. The Page

Well...I'ts hoisting after all

Gajender Tyagi — Thu, 12 Aug 2021 04:29:28 +0000

Well the image is self explanatory. You can get an idea of lexical scope of const and how does hosisting work for const.

For some extra fun change const with --var--

Microsoft's Node.js course review

Gajender Tyagi — Sun, 09 Aug 2020 08:54:54 +0000

The course 📘

Recently on Microsoft learn a new course was introduced giving knowledge on node.js. Over the previous weekend I took the course to have a look at the quality and depth off the content.

Although the course says its for beginner 🚁 but if you are an absolute beginner then you might have a bit of difficulty catching up with the course. But you can catch up with it by googling the concepts you are not ware of.

Unlike some of the course which starts directly with creating a http server this course teaches first the core concepts of node.js and understanding of which is quite important if ou want to move to advance level, its better to build these core concepts from start which this course does nicely.

There are 5 modules in this course and as per Microsoft its a 2hr 44mins course but that's just reading time you would need more time to process that information. It took me 4 hours to complete this course which included reading the content, doing practice exercises and reporting few of the error I could find in the course material.

I think one should go through this course to revise his concepts.

I liked the content of the course, the practice examples and the interface of the learn website. 🍻
Yes, there were few issues in the code which I could figure out and reported to Microsoft learn also made a PR on there GitHub repo.
🪂

The link to the course 🚀

GitHub link

registerationForm

Gajender Tyagi — Sun, 07 Jun 2020 08:22:21 +0000

Well JARF (just another registration form) 😃

I Would love ❣️ it if you guys can share similar simple code for form generation.

Unary operators in C | सी में अनियोजित ऑपरेटर ➕➕

Gajender Tyagi — Wed, 06 May 2020 16:47:09 +0000

This is for my ❤️ Rashi as she is learning coding 💻 I wanted to help her understand concepts in the best way I can.🚀

Using hindi translation with English.

What are Unary operators in c and 🤔 why do we need to learn them?

First we need to understand what is an operator?

पहले हमें यह समझने की जरूरत है कि एक ऑपरेटर क्या है?

Simply put an operator is a symbol used to perform a mathematical or logical manipulation on operand.
सीधे शब्दों में कहें तो एक ऑपरेटर एक प्रतीक है जो ऑपरेंड पर गणितीय या तार्किक हेरफेर करने के लिए उपयोग किया जाता है।
e.g.
- unary minus(-)
- increment(++)
- decrement(- -)
- NOT(!)
- Addressof operator(&)
- sizeof()

What is an operand?

एक ऑपरेंड क्या है?

The argument(variable) on which operator acts upon is an operand.
वैरिएबल जिस पर ऑपरेटर कार्य करता है वह एक ऑपरेंड है।
e.g. -b: In here minus(-) is an operator and 'b' is an operand. a++: In here ++ is an operator and 'a' is an operand.
In the above example -b, the minus is giving a negative value to b and in a++ the increment operator(++) is changing the value of a by increment to +1 value. a++ can be written as a = a + 1.

We will look at each of operands and their uses.

हम प्रत्येक ऑपरेंड और उनके उपयोगों को देखेंगे।

Unary minus(-)

Most of us must have first learned about negative numbers in 6th class, as it was taught then the same applies in programming as well. A unary minus changes the sign of its argument(variable).

हम में से अधिकांश ने पहले 6 वीं कक्षा में नकारात्मक संख्याओं के बारे में सीखा होगा, क्योंकि यह सिखाया गया था और साथ ही साथ प्रोग्रामिंग में भी लागू होता है। एक अनुपस्थित माइनस अपने तर्क (चर) के संकेत को बदलता है।

Code to explain ....

 int number1 = 10;
 int number2 = -number1;  // number2 = -10

In above code the operator '-' changes value of +10 to -10.
उपरोक्त कोड में ऑपरेटर '-' +10 से -10 का मान बदलता है।

Similarly ....

 int number1 = -10;
 int number2 = -number1;  // number2 = 10

If applied on a negative number the result will be positive as - + - = +.
यदि माइनस नंबर पर आवेदन किया जाता है तो परिणाम सकारात्मक होगा - + - = +।

Increment(++)

It is used to increase the value of operand by 1. You must be familiar with the mathematical operations such as 4+1 = 5, in c language you must have seen a = a + 1
इसका उपयोग 1 से ऑपरेंड के मूल्य को बढ़ाने के लिए किया जाता है। आपको गणितीय क्रियाओं जैसे 4 + 1 = 5 से परिचित होना चाहिए, सी भाषा में आपने a = a + 1 जरूर देखा होगा।

int number = 5; 
number = number + 1 // number = 6

In the same manner increment operator works.
उसी तरीके से इंक्रीमेंट ऑपरेटर काम करता है।

int number = 5; 
number++; // number = 6

decrement(- -)

It is opposite of increment operator. It will decrease the value of operand by 1.
यह प्लस ऑपरेटर के विपरीत है। यह 1 से ऑपरेंड के मूल्य में कमी करेगा।

int number = 6;
int number = number - 1; // number = 5

In the same manner decrement operator works.
उसी तरह माइनस माइनस ऑपरेटर काम करता है।

int number = 5; 
number--; // number = 5

I'm leaving the concept of post and pre increment and decrement for now as understanding one concept before another is important.

**मैं पद और पूर्व वेतन वृद्धि और वेतन वृद्धि की अवधारणा को छोड़ रहा हूं क्योंकि एक अवधारणा को दूसरे से पहले समझना महत्वपूर्ण है। **

NOT(!)

The logical state of an operand is changed by the not operator and it is represented by !.

A value which is true is changed to false and vice-versa.
एक मान जो सत्य है, उसे असत्य और इसके विपरीत में बदल दिया जाता है।

In C language you must have studied about boolean data type, if not please click here.

If x is true, then !x is false If x is false, then !x is true

Code example....

bool value = true;
bool value2;
value2 = !value // value2 = false

in progress........

Reference article: https://www.geeksforgeeks.org/unary-operators-cc/

Var, Const, Let declaration and initialization 💻🚀

Gajender Tyagi — Sat, 25 Apr 2020 09:21:32 +0000

I have used a basic function ⚙️ to show how variable declaration works in js.

Currently the code is on fire 🔥 Try to run 🏃‍♀️ the below codes and correct ✔️ the errors ❌ to save it from burning 🚒.

The code is self explanatory. 🌳

1 🔥


function variables(){
  console.log(`This will explain us if variables declared as 'const' are hoisted or not,
               value of a = ${a}`);
  const a ;// const declaration  
  console.log(`a after declaration but no value is initialized, can this be done ?
               a = ${a}`);
  a = 'aa'; // initialized const 
  console.log(`a after value is assigned, a = ${a}`);

  console.log(`Hoisting of variables declared with 'var' keyword can be seen here,
               value of b = ${b}`); 
  var b = 'bb' ; // initialize a with a value
  console.log(`We can see here that b is no more undefined, values of b = ${b}`);

  console.log(`This will explain us if variables declared as let are hoisted or not,
                value of c = ${c}`);
  let c ;
  console.log(`c after declaration c = ${c}`);
  c = 'cc'; 
  console.log(`c after values initialized is  c = ${c}`);
}

variables();

SyntaxError: missing = in const declaration

2 🔥


function variables(){
  console.log(`This will explain us if variables declared as 'const' are hoisted or not,
               value of a = ${a}`);
  const a = 'aaa'; // const declaration  
  console.log(`a after declaration but no value is initialized, can this be done ?
               a = ${a}`);
  a = 'aa'; // initialized const 
  console.log(`a after value is assigned, a = ${a}`);

  console.log(`Hoisting of variables declared with 'var' keyword can be seen here,
               value of b = ${b}`); 
  var b = 'bb' ; // initialize a with a value
  console.log(`We can see here that b is no more undefined, values of b = ${b}`);

  console.log(`This will explain us if variables declared as let are hoisted or not,
                value of c = ${c}`);
  let c ;
  console.log(`c after declaration c = ${c}`);
  c = 'cc'; 
  console.log(`c after values initialized is  c = ${c}`);
}

variables();

ReferenceError: can't access lexical declaration 'a' before initialization

3 🔥


function variables(){
 //  console.log(`This will explain us if variables declared as 'const' are hoisted or not,
 //               value of a = ${a}`);
  const a = 'aaa'; // const declaration  
  console.log(`a after declaration but no value is initialized, can this be done ?
               a = ${a}`);
  a = 'aa'; // initialized const 
  console.log(`a after value is assigned, a = ${a}`);

  console.log(`Hoisting of variables declared with 'var' keyword can be seen here,
               value of b = ${b}`); 
  var b = 'bb' ; // initialize a with a value
  console.log(`We can see here that b is no more undefined, values of b = ${b}`);

  console.log(`This will explain us if variables declared as let are hoisted or not,
                value of c = ${c}`);
  let c ;
  console.log(`c after declaration c = ${c}`);
  c = 'cc'; 
  console.log(`c after values initialized is  c = ${c}`);
}

variables();

TypeError: invalid assignment to const 'a'

4 🔥


function variables(){
 //  console.log(`This will explain us if variables declared as 'const' are hoisted or not,
 //               value of a = ${a}`);
  const a = 'aaa'; // const declaration  
  //console.log(`a after declaration but no value is initialized, can this be done ?
  //             a = ${a}`);
  //a = 'aa'; // initialized const 
  console.log(`a after value is assigned, a = ${a}`);

  console.log(`Hoisting of variables declared with 'var' keyword can be seen here,
               value of b = ${b}`); 
  var b = 'bb' ; // initialize a with a value
  console.log(`We can see here that b is no more undefined, values of b = ${b}`);

  console.log(`This will explain us if variables declared as let are hoisted or not,
                value of c = ${c}`);
  let c ;
  console.log(`c after declaration c = ${c}`);
  c = 'cc'; 
  console.log(`c after values initialized is  c = ${c}`);
}

variables();

ReferenceError: can't access lexical declaration 'c' before initialization

console log: a after value is assigned, a = aaa Hoisting of variables declared with 'var' keyword can be seen here, value of b = undefined We can see here that b is no more undefined, values of b = bb

5 🧯


function variables(){
 //  console.log(`This will explain us if variables declared as 'const' are hoisted or not,
 //               value of a = ${a}`);
  const a = 'aaa'; // const declaration  
  //console.log(`a after declaration but no value is initialized, can this be done ?
  //             a = ${a}`);
  //a = 'aa'; // initialized const 
  console.log(`a after value is assigned, a = ${a}`);

  console.log(`Hoisting of variables declared with 'var' keyword can be seen here,
               value of b = ${b}`); 
  var b = 'bb' ; // initialize a with a value
  console.log(`We can see here that b is no more undefined, values of b = ${b}`);

  //console.log(`This will explain us if variables declared as let are hoisted or not,
  //              value of c = ${c}`);
  let c ;
  console.log(`c after declaration c = ${c}`);
  c = 'cc'; 
  console.log(`c after values initialized is  c = ${c}`);
}

variables();

no errors this time 😀

console log:
a after value is assigned, a = aaa Hoisting of variables declared with 'var' keyword can be seen here, value of b = undefined We can see here that b is no more undefined, values of b = bb c after declaration c = undefined c after values initialized is c = cc

Finally !!!🎉🎉 we have seen 👀 how to declare and initialize variables with var, let and const keywords in JS.

I would request the reader to comment out what all he learned from this post and if there are any mistakes please point them out as well with code sequence number. Thanks 🙏