DEV Community: Rahul Ghosh

Simple JS Interview Questions for All Beginners.

Rahul Ghosh — Sat, 08 May 2021 15:36:20 +0000

1 Null Vs Undefined

A null means absence of a value. It means we can define a variable but have not assigned any value, so the value will be absent.
Otherside, Undefined is also a primitive value in JavaScript. A variable or an object has an undefined, when we have no value is assigned before we use it.

2 double equal (==) and triple equal (===) in javascript.

Double equals use for value equality. This means that before checking the values, it converts the types of the variables to match each other.
Triple equals do not perform type coercion. It will verify whether the variables compared have both the same value and the same type.

3 global variable, global scope

In JavaScript, there are two types of scope. Local scope Global scope. When variables are declared within a JavaScript function, it’s called local scope. In local scope, variables are only used only inside their functions
A variable declared outside a function, its called global scope. All other scripts and functions can access these global scope variables.

4 call(), apply() and bind() method

As functions are also objects in JavaScript, call(), apply() and bind() are used to control the function invocation. You can use call() or apply() to invoke the function immediately. bind() returns a bound function. So bind() can be used when the function needs to be called later.

5 let and const

ES6 introduced two new types of variable declarations in JavaScript.The keywords let and const. The let declarations is the same syntax as var declarations. Unlike variables declared with var, variables declared with let have a block-scope. let does not create any global property on the window. let reassignable and not redeclare.
Const is similar to var or let declarations. The const makes a variable a constant where its value cannot be changed. Const variables have the same scoping rules as let variables.

6 Arrow Function

In ES6, introduced us to write shorter function syntax which is Arrow functions. It allows us to create functions in a cleaner way similar to regular functions.

7 DOM

DOM means Document Object Model. DOM is use for programming interface for HTML and XML documents. The DOM represents a document as a tree of nodes. The DOM is cross-platform and language-independent ways of manipulating DOM tree.

8 API

API means Application Programming Interface. An API is a set of functions that allows applications to access data and interact with external software components, operating systems, or microservices.

9 callback function

JavaScript runs code sequentially in top-down order. The way to create a callback function is to pass it as a parameter to another function, and then to call it back right after something has happened or some task is completed.

10 This keyword

In Javascript, this keyword is an important confusing keyword. In an object method, this refers to the owner of the method. It has different values depending on where it is used. This points to a particular object. Now, which is that object depends on how a function that includes 'this' keyword is being called.

React.js primary concepts for beginner.

Rahul Ghosh — Fri, 07 May 2021 11:53:07 +0000

1 What is React...?

React is a JavaScript library, not a framework. React is use for building user interface. React use more libraries for any solution.
Frameworks use for great purpose, especially for young developers. Framework already has smart design for you. When you need small piece of code, you have to include the whole thing anyway. UIs are everywhere, from the simple buttons on a microwave to the dashboard of a space shuttle. React is good for developed UI. React have virtual DOM, thats why react is best for modern developer.

2 React JSX

JSX means Javascript and XML. JSX allows us to write HTML in React. JSX makes it easier to write and add HTML in React. It is faster because it performs optimization while compiling code to JavaScript. It is also type-safe and most of the errors can be caught during compilation. JSX easier and faster to write templates, if you are familiar with HTML.

3 React is all about components

In react everythings are component base. React has two type of component one is class component another is functional component. Component are small piece of reusable, composable, and stateful codes. React components are exactly the same; their input is a set of props and their output is a description of a UI. We can reuse a single component in multiple UIs. Components can contain other components. React component can have a private state. Those state to hold data. This private state is an implicit part of the input that drives the component’s output.

4 React DOM

React DOM means Document Object Model. In react has a virtual DOM. A virtual DOM object is a representation of a DOM object, like a lightweight copy. Manipulating the DOM is slow. Manipulating the virtual DOM is much faster, because nothing gets drawn onscreen. Think of manipulating the virtual DOM as editing a blueprint, as opposed to moving rooms in an actual house.

5 React defaultProps

React components take inputs in the props argument. Then passed down from the Parent component. The child component will access them from the props object with the attribute name serving as the key. The problem here is what happens if the parent component doesn’t pass any attributes to the child component? Sure we will see undefined display in place of the props not sent by the parent component. To solve this issue, we can use the logical operator to set a fallback value, so when a prop is missing it displays the fallback value in place of the missing prop.

6 React optimizing Performance

Performance is important for any project. Clients wants their application have too much faster. Thats why's react is much concern of performacne. If you’re faceing performance problems in your React apps, make sure you’re test. React includes many helpful warnings. These warnings are very useful in development. You can read this warning and find the problem easily

7 React State

React has a built-in state object. Where store property and values that belongs to the component. When the state changes, the component will be re-renders. State contain as many properties. You can changes the state values by setState function. Always use the setState() method to change the state values, it will ensure that the component knows its been updated.After that it calls the render() method again,

8 Conditional rendering

In JSX when we thing conditional rendering, Ternary operator come out first in oor mind. In conditional rendering ternary operator vary helpful to us, its give two value depend on true false condition.

9 How rendering works

Every setState function call react state to change new State. Then react call render method to update the components in memory (DOM). Raect compares it with browser. If there are any changes, React does the smallest possible update to the DOM.

10 Raect props

Props means property. Props are used for passing data from one component to another. Parent component pass values to children using props.

10 Basic Topic For Beginner JS programmer.

Rahul Ghosh — Thu, 06 May 2021 15:30:07 +0000

1 Types of Javascript

JavaScript has data types. In the programming world, data types are an important concept. Actually, javascript differ their type in two way “Primitive Values” and “Object”

Some primitive data type is

i strings
ii number
iii boolean
iv undefine
v null

Object are
i object
ii function

2 What we do when errors happen!!!

Sometimes when executing JavaScript code, different errors can occur. So what do we do?
Javascript have a special error handler TRY and CATCH

The ‘try’ statement checks the block of code to be tested for errors while it is being executed and if an error occurs in the try block the ‘catch’ statement catches the block of code to be executed.

3 Coding Style for every programmer

Make sure to always use the same coding style in your projects. Use camelCase for identifier names in variables. It's a good variable name that starts with letters.

For functions :
Put the opening bracket at the end of the first line. Use one space before the opening bracket. Put the closing bracket on a new line, without leading spaces. Do not end a complex statement with a semicolon.

For Object :
Place the opening bracket on the same line as the object name. Use colon plus one space between each property and its value. Use quotes around string values, not around numeric values. Do not add a comma after the last property-value pair. Place the closing bracket on a new line, without leading spaces. Always end an object definition with a semicolon.

4 Comment

JavaScript comments are useful to explain code and to make it more readable.
It can be written two ways single line comment and multi-line comment

5 Arrow Function

We are familiar with arrow functions in ES6. Arrow functions make it easier to write shorter syntax. Modern programmers used to like it. If you check today's date by arrow function to write.

6 Spread Syntax (...)

The spread syntax can be used when all elements from an object or array need to be included in a list of some kind. It is much easier to include all previous items or lists them into a new array or object.

7 `Default Parameters of functions

Sometimes we have a situation where we find undefined value in our output. In JavaScript, default function parameters are solved to initialize named parameters with default values if no values or undefined are passed into the function.

8 JavaScript Hoisting

Variable hoisting plays an important role in programmer life. Actually, a beginner programmer faces too much when writing code. Hoisting is JavaScript's default behavior of moving all declarations to the top of the current scope. the variable can be declared after it has been used. Another side a variable can be used before it has been declared.

9 ES6 Symbol data type

The symbol is a primitive datatype just like Number, String, or Boolean. Symbols are always unique. For instance, if different coders want to add a person.id property to a person object belonging to a third-party code, they could mix each other's values.

10 cross-browser testing

Sometimes a developer needs to test the project on various platforms to check how to run the project. If A developer develops a web application first and needs to test various browsers. If it works well after that it's definitely works for the real world.

Some Regular JavaScript Methods for JS Developers...

Rahul Ghosh — Wed, 05 May 2021 15:38:13 +0000

Use of extracting string method

1 slice(start, end) Method

The Slice method takes two parameters, the first one where the extract starts position, and the last one extract end position. The Slice method is used when some specific string is extracted in a string. If a parameter is negative, the position is counted from the end of the string. If you do not use the second parameter, the result will slice out the rest of the string. Slice can accept negative indexes.

2.substring(start, end) Method

substring() is the same to slice() Method. The difference between substring() cannot accept negative indexes. This method also has two parameters first one is extracted start positions and the last one is extracted end position.

3 substr(start, length) Method

substr() is also the same as slice() But the difference is that the second parameter specifies the length of the extracted part. If you omit the last parameter, the result will slice out the rest of the string.

Use of number method

4 parseInt() Method

The parseInt() method parses a string. This method returns a whole number. These method spaces are allowed. Only the first number is returned.

5 parseFloat() Method

The parseFloat() method converts strings to numbers. If the number cannot be converted, NaN (Not a Number) is returned. This method is used in regular needs.

Use of Math method

6 Math.abs() Method

The Math.abs() returns the absolute (positive) value of x . When you need a positive value from a negative number it is a helpful method for a developer.

7 Math.pow() Method

Math.pow(x, y) returns the value of x to the power of y. This is a built-in method in Javascript Math.

Use of array method

8 Pop() method

Array in js plays an important role in development. Pop() is a built-in method of javascript. The pop() method removes the last element from an array. This is a method of the array.

9 Push() method

Sometimes we need to add some items in an array, so what we do that time! The push() method adds a new element at the end to an array. This method returns the new array length.

10 shift() method

The shift() method removes the first array element and "shifts" all other elements to a lower index. This array method is similar to pop() but different from removing item position.