What is hoisting in the javascript.

RahulMandyal — Thu, 14 Apr 2022 03:10:19 +0000

Hoisting is very important and tricky part in the javascript world .When a program loads into the js engine for execution it will not executed in the same way as we have writeen it.

*Hoisting * means during the declaration phase it will hoist (raise) all the variable declaration and function declaration to the top of the current scope .
Let, s understand it with the help of a example :

In the above example you have seen as we have writeen our program is not executed in the same way by the Javascript engine .So now its time to go more deep .Then you all will be able to understand why this happened.

When the js engine execute the code it will creates a global execution context and it has two phases .

First Phase(Declaration phase) :
In the first phase (declaration phase ) it will allocate memory to all the variables and function .
Highest priority is given to the function declaration. Javascript engine will move all the function declaration to the top .
Like this :

var keyword :
During the Execution phase variable declared with var keyword are initialized with undefined value whereas variable declared with let and const keyword are initialized during the execution time only but memory is being allocated to all the variables during the declaration phase only.

let and const keyword

But if your write the above same code and replace the var keyword with let and const then it will throw an error Because you can,t access a variable which is not initialized yet. Because variables declared with let and const are initialized during the execution phase only.

Function expressions
Function expressions are not treated as the same as function declaration .During the declaration phase they are treated as a variable .

Execution Phase
In the execution phase it will execute code line by line means synchronously . The reason why it will execute all the code line by line is that Javascript engine is single threaded .

I hope now all of you are able to understand what is hoisting in javascript .this article will must help you to understand this topic :)

All you need to know about object destructuring

RahulMandyal — Sat, 09 Apr 2022 20:04:40 +0000

As we all know javascript es6 version had came with a lot of feature and it made javascript slightly better .Object destructring also came with the es6 version it somehow also made our job easier .

Before es6 version when we want to assign object properties into a variable we typically do it like this:


let user = {
  name : "Rahul thakur",
  age : 19
};
let userName = user.name;
let userAge = user.age;

But now object destructuring provides us better syntax that can help us to reduce our code and also provide an alternative way to assign properties of an object to a variable:

let {name : username , age : userage} =user;

the syntax is :
{let property1 :variablename , property2 : variablename}= object ;

Make your code more shorter:

If your variable have the same name as the properties of the object then we can make our code more shorter
let {name , age } = user ;``
this is equivalent to the previous one.now instead of writing two two lines of code we can do it within one line of code .

undefined values :

Suppose you are trying to assign a property that does not exits in the object then then variable is set to undefined for example :

Here in this example phone ,lastname,email is not present inside the user object so those variable which are not present inside the obejct are initialized with the undefiend value.

Setting default values

we can assign a default value to the variable if the property does not exits inside the the object then instead of undefined the variable is initialized with the default value for example :

Summary

Object destructuring just making our job easier .It provides us better syntax to store object properties value inside variables with in one line of code .

DEV Community: RahulMandyal

What is hoisting in the javascript.

All you need to know about object destructuring