React JS Interview Questions and Answers | HopeTutors

1: What is React JS ?
Answer
React JS is an Open Source Javascript Library Primarily used for forming user interfaces precisely for Singular Page Applications.Facebook Developers Created the React JS in 2011 and up to now it was widely used and garnered a large community of learners and developers.
Answer : Error Boundaries are primarily used for acquiring Javascript errors anywhere in the Child Components. Logging the errors and Projecting the Fallback UI was its major Usage.
Answer :
List Elements would be assigned with stable identity by the help of Keys.These keys are unique. Mostly the ID of the data would be used as the Key.
Answer : Based on logic rendering will happen.If particular condition is met then we shall render the page.

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Answer :User Actions like Mouse Clicks, Keypress would be considered as an Event. Event Contains a set of different properties.
Answer :
There is no way to create a list without key for element, if it is bound to happen there would be errors in the rendering. The browser console too throw back an error.
Answer : In Case of Multiple States sharing the Common data, there is a possibility to lift up the state to its Closest Common Ancestor. Parents hold the Common state where the Child do not hold any state. Child and Parent Components would use the same state.
Answer :
Grouping of Child Component without the use of Additional Node is called Fragment.
Answer
The Higher Order Component is the function that intake a component and return a new component.For Reusing the Component logic, the higher order component function is used.
Answer :The Mode that is used for running additional Checks and Warnings for React Components.It do not affect production build since it runs only on development build. It would highlight the application problem in User Interface.
Answer :Empty tags are primarily used to declare the fragments in React.
Answer :Passing of Data through a tree of react components is called react context.This Context is used to share data globally between two react components.
Answer :Provision of Values to the context is called Context provider.These values can be used by any other components in the application. Context Consumers are primarily used for reading the values.

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Answer :Learning curve :

Students with strong Javascript, Cascading Styling Sheet Understanding can be able to learn react with ease.

Code Readability :

The JSX Usage marginally enhances the code readability.

Performance :

The Virtual DOM presence accelerates the performance since Updating UI do not require the entire website to all single changes.
Reusable components :

Single Component can be used at multiple places at no need of code rewriting.

Server Side Rendering ( SSR ) :

The Server Side Rendering was Supported by React and it also enhances the loading time of webpages.

Answer :Rendering of Web page in the server whereas usually it will be applied on browser, this process is called as Service Side Rendering.It improves the page loading speed and also performance,SEO, User Experience to Web Pages.
Answer :The JSX is the syntax extension of JavaScript and used to create the React elements. These elements are then rendered to the React DOM.
Answer : Real DOM Manipulation would make the application much slower, there would be a Virtual DOM for every assigned Real DOM. Virtual DOM offers similar features and it can be Manipulate much faster than Real DOM.
Answer :JSX is dissimilar to the Javascript, Since browsers only read Javascript files. Babel is primarily used to transform JSX code into the Javascript Objects.

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Answer :The Building Blocks of React Application are Called React Components.It is basically a function that takes the inputs which are called as props would return back the elements of react that should need to be projected on the screen.Components let you to split the UI into Independent and Reusable Pieces.
Answer :The major two types of Components in the React are
The first one is called as Function Component
The Second one is known as Class Component
Answer :Brief about the Function Component

The Javascript Functions where a react element would be returned with the input properties are called Function Component.

Class Component

The Javascript ES6 class that extend to React.Component are called Class Component.

Answer :
When dealing with state wise or life cycle methods, the Class components in the react would be used.
Answer :The Object that defines the rendering and behaviour of component is React ‘State’. Component private party is the state and also stores information that changes over time of the component. Regarding the state value, UI would be updated by react components.
Answer :For passing the data to a component the props are used. Single or Multiple values can be passed to the component.It is primarily used for passing component data and make any changes in the state.
Answer :The Duo State and the Props holds the information about the react component.State objects are available inside the component.In other hand props are utilized to send data from component to another component.

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Answer :State can be updated Directly or Indirectly. If there is a case to update directly, the UI Element that was linked to the state would not be Updated. The best way to do that is use setState method, this involves the Updation of State Object and Automatic re rendering of the Component.
Answer : The Component that do not holds any state is Called as Stateless Component. It would take Props as argument and returns a react element on the values of ‘props’.There is no existence of Lifecycle for these Components
Answer :Component that hold only one state which is used for UI rendering are called Stateful Component. They are generally referred as Class Components.
Answer :React.createElement is primarily used to build one react element that can be used as a User interface component. CloneElement is mostly used for cloning the element.
Answer :‘setState’ function was primarily used for updating the state of a react component. In the case of UI component dependency regarding the value we are going to update,the UI will get re-rendered.
Answer :The Middleware that allows the coder to add the creator action that revert the functions rather than the actions is Redux.The other purpose to use this was as a delay function like delaying the action dispatch only if some condition is met. getState() and dispatch() are inner function parameters.

To Activate the Redux,Middleware() method was applied.

Answer :
Flux is generally an illustration which is useful in managing the single directional data stream. These are meant to be controlling the data fragments and make them to interfere with the data without issues.Flux is not specified to any react application or collection of react application
Answer :Server needs frequent monitoring for the updates with the time.The general case would be to know whether novel comments are present or not, this process is commonly known as pooling. It would check for updates for every 5 seconds and we can also change the time period with ease.It can create issues that is related to the things that are happening, thus pooling is considered.
Answer :Complex tasks can be easily handled by the React JS. No need to care of the bus while performing the tasks, there by error free outcomes and developing scalable apps.It is growing technology with learners and developers, we can rely on its quality outcomes.
Answer :Applications which are developed using flux have the components that can be tested easily. We can manage and test any react component by updating the store thereby decreasing the risk of data affection. These applications are scalable and holds no compatibility issues.
Answer :ReactJS would transform the browser events thereby monitoring their behaviour. The primary purpose to do this is events should hold the logical properties even the browsers are different, in layman words ReactJS is like logical event system cross-browser.
Answer : The case components that are rendering two times, Virtual DOM would check the modification elements, the elements that needs to change was represented, there are multiple elements that don’t go through the changes. DOM doffing is used to cut DOM changes, it generally improves the browser performance, this pave the the browser a way to perform all tasks at a quicker pace.
Answer :There is a case of possibility, it is like HTML Elements Nestation. The limitation would be there are things that are different in it, need to have good knowledge towards the elements like source and destination to complete the task quickly.
Answer :There is a need of one JSX Element which helps the task to be completed easily, if there is the existence of multiple expressions the process would get slow, people who are new to the technology would get confused if there are multiple expressions present in it.

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Answer :The below mentioned steps gives an idea on how react actually works,

Diffing algorithm would be run by React to identify changes that need to be made in Virtual DOM.
The next step would be used to update the DOM as per new features which is Reconciliation.
Virtual DOM that is too light in nature would be detached from specific implementations of the browser.
Virtual DOM Elements would be used to build basic nodes
After the Component Change in State, Diffing algorithm would run quicker and identify changes.After the changes has been identified, it would automatically update the DOM with the Change difference.

Answer :No, It only uses JSX which is similar to HTML.

Answer :
ReactJS too holds lot of limitations like other platforms, the major drawback would be the library size, being complex would create a lot of uncertainty among the code developers.The inline templating with JSX also adds voice, most importantly the one only one layer of app is covered.In order to develop the app, developers rely on multiple technologies that take time.
Answer :A Controlled Component would take the current value through props and notify the changes with callbacks like onChange. The Parent component “controls” by handling the callback and managing its own state and passing the newer values as props to the controlled component. This is also called as “dumb component”.
An Uncontrolled Component stores its own state internally and need to query the DOM using a reference to find the current value when you need to find it, it is similar to the HTML.
Answer :React router decides the components that needs to be rendered and also components that not needs to be rendered.Dictation is also performed by Router for various activities.
Answer :Applications which are developed using flux have the components that can be tested easily. We can manage and test any react component by updating the store thereby decreasing the risk of data affection. These applications are scalable and holds no compatibility issues.
Answer :ReactJS would transform the browser events thereby monitoring their behaviour. The primary purpose to do this is events should hold the logical properties even the browsers are different, in layman words ReactJS is like logical event system cross-browser.
February 4, 2020
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