(1).Truthy and Falsy values

Md. Ilahi Hossain Shiblu
2 min readMay 8, 2021


(2).Null vs Undefined

Null is a special value which means there is no value. Null is a special object because typeful null gives the object. On the other hand, the undefined means that the variable has not been declared or given any value.

(3).scope, block scope

Scope to any variable in the case of your code or other determines the accessibility of the organization.

A block scope is the area where switches to conditions or loops and when.
Generally speaking, when you have {curly brackets} you see, it is a block.

(4.)bind, call and apply

Bind (): Gives you a new function allowing you to pass an array and a number of arguments.

Call (): The call () method provides a given value and argument one by one.

Apply (): Prays for the function and allows you to pass arguments as arrays.

(5).understand the this keyword

This keyword for a function is unnecessarily different in JavaScript than in other languages. Strict mood and no strict there are also some differences in mood.

(6).setTimeout, setInterval

setTimeout(): Execute a block only once the specified time has elapsed.

setInterval(): Repeat a specific block of code with a specific time delay in each call.

(7).DOM (Document Object Model )

Document Object Model (DOM) HTML and XML a program interface for documents. It represents the page so that programs can change the structure, style and content of the document.

(8).callback function

A callback function is a function that is passed as another function argument Which is then called to the inside of the external function to complete any kind of routine or curry.

(9).what is an API

API is an acronym for Application Programming Interface which allows the two applications to talk to each other.


A closure is a combination of connected functions associated with the lexical environment of the surrounding state.