Thunk Interview Questions for Freshers/Thunk Interview Questions and Answers for Freshers & Experienced

Why is setState in react asynchronously?

This is because setState changes the state and triggers reconfiguring. This may be a costly process, and making it synchronous may cause the browser to become unresponsive. As a result, setState calls are both asynchronous and batch-processed for improved UI experience and performance.

What is a virtual DOM in React?

The virtual DOM (VDOM) is a programming concept in which an ideal, or “virtual,” version of a user interface (UI) is stored in memory and synchronized with the “real” DOM using a library such as ReactDOM. They may also be regarded as a component of React’s “virtual DOM” implementation

What are the downsides of Redux compared to Flux?

* You will need to learn to avoid mutations: Flux is un-opinionated about mutating data, but Redux doesn't like mutations and many packages complementary to - - Redux assumes you never mutate the state. You can enforce this with dev-only packages like redux-immutable-state-invariant, Immutable.js, or instructing your team to write non-mutating code.

* You're going to have to carefully pick your packages: While Flux explicitly doesn't try to solve problems such as undo/redo, persistence, or forms, Redux has extension points such as middleware and store enhancers, and it has spawned a rich ecosystem.

* There is no nice Flow integration yet: Flux currently lets you do very impressive static type checks which Redux doesn't support yet.

What is the meaning of Babel in react?

Babel is a JavaScript interpreter. Babel is a toolchain that is mostly used to transform ECMAScript 2015+ code into a backwards-compatible version of JavaScript that can be used in both current and previous browsers or environments.

Why are Redux state functions called reducers?

Reducers always return the accumulation of the state (based on all previous and current actions). Therefore, they act as a reducer of state. Each time a Redux reducer is called, the state and action are passed as parameters. This state is then reduced (or accumulated) based on the action, and then the next state is returned. You could reduce a collection of actions and an initial state (of the store) on which to perform these actions to get the resulting final state.

What is the mental model of redux-saga?

Saga is like a separate thread in your application, that's solely responsible for side effects. redux-saga is a redux middleware, which means this thread can be started, paused and cancelled from the main application with normal Redux actions, it has access to the full Redux application state and it can dispatch Redux actions as well.

How Relay is different from Redux?

Relay is similar to Redux in that they both use a single store. The main difference is that relay only manages state originated from the server, and all access to the state is used via GraphQL queries (for reading data) and mutations (for changing data). Relay caches the data for you and optimizes data fetching for you, by fetching only changed data and nothing more.

Can Redux only be used with React?

Redux can be used as a data store for any UI layer. The most common usage is with React and React Native, but there are bindings available for Angular, Angular 2, Vue, Mithril, and more. Redux simply provides a subscription mechanism which can be used by any other code.

What are the advantages of formik over redux form library?

Below are the main reasons to recommend formik over redux form library:

* The form state is inherently short-term and local, so tracking it in Redux (or any kind of Flux library) is unnecessary.

* Redux-Form calls your entire top-level Redux reducer multiple times ON EVERY SINGLE KEYSTROKE. This way it increases input latency for large apps.

* Redux-Form is 22.5 kB minified gzipped whereas Formik is 12.7 kB

What is route based code splitting?

A good place to start code splitting is with app routes. Break down an application into chunks per route, and then load that chunk when user navigate that route. Under the hood, webpack takes care of creating chunks and serve chunks to the user on demand.

Can we make changes inside child components?

Yes, we can make changes inside the child component in Props but not in the case of States.

Explain Presentational segment

A presentational part is a segment which allows you to renders HTML. The segment’s capacity is presentational in markup.

What is the difference between createElement and cloneElement?

createElement is the thing that JSX gets transpiled to and is the thing that React uses to make React Elements (protest representations of some UI). cloneElement is utilized as a part of request to clone a component and pass it new props. They nailed the naming on these two.

How do you tell React to build in Production mode and what will that do?

You set process.env.NODE_ENV to production. When React in production mode, it’ll strip out any extra development features like warnings.

Why is switch keyword used in React Router v4?

Within the Switch component, Route and Redirect components are nested inside. Starting from the top Route/Redirect component in the Switch, to bottom Route/Redirect, each component is evaluated to be true or false based on whether or not the current URL in the browser matches the path/from prop on the Route/Redirect component. Switch is that it will only render the first matchedchild.

What do you understand by “Single source of truth”?

Single source of truth (SSOT) is the practice of structuring information models and associated data schema such that every data element is mastered (or edited) in only one place. Redux uses Store to store the entire state of the application at one location. So all the state of the component is stored in the store and the store itself receives updates. The single state tree makes tracking modifications simpler over time and debugging or inspecting the request.

What’s the difference between an Element and a Component in React?

Simply put, a React element describes what you want to see on the screen. Not so simply put, a React element is an object representation of some UI.

A React component is a function or a class which optionally accepts input and returns a React element (typically via JSX which gets compiled to a createElement invocation).

Explain DOM Diffing in React.

The process of checking the difference between the new VDOM tree and the old VDOM tree is called "diffing". Diffing is accomplished by a heuristic O(n) algorithm. During this process, React will deduce the minimum number of steps needed to update the real DOM, eliminating unnecessary costly changes. This process is also referred to as reconciliation.

What is Action?

Actions are plain JavaScript objects and they must have a type property to indicate the type of action to be carried out. They must also have a payload that contains the information that should be worked on by the action.

What can you do if the expression contains more than one line?

In such a situation, enclosing the multi-line JSX expression is an option. If you are a first time user, it may seem awkward but later you can understand everything very easily. Many times it becomes necessary to avoid multi-lines to perform the task reliably and for getting the results as expected.

What is the purpose of the constants in Redux?

When you use an IDE, the constants allow you to find all the usages of specific functionality across the project. It also prevents you from making silly mistakes which are usually caused by typos; in that case, you will receive a Reference Error immediately.

What are reducers in redux?

The reducers in redux are the pure functions that take the previous state and an action, and then it returns to the next state.
(previousState, action) => newState

It is known as the reducer because they are the type of function that would pass to Array.prototype.reduce(reducer, ?initialValue). It is very essential to ensure that the reducer stays pure.

Tell me the redux workflow features?

* Reset: Allow resetting the state of the store
* Revert: Rollback to the last dedicated state
* Sweep: All disabled actions that you might have fired by error will be detached
* commit: makes the present state the initial state

What are the important Redux Terminology?

1. Store
2. Reducer
3. Action
4. Action Creator
5. Dispatch
6. Subscribe
7. Provider
8. Connect

What are the downsides of Redux compared to Flux?

Instead of downsides, there are few compromises of using Redux over Flux that is listed below:

* You need to learn the avoiding of mutations: Flux is un-opinionated about mutating the data, however, Redux does not like mutations, and most of the packages which are complementary to Redux should never alter the state.

* You have to carefully pick your packages: While Flux principle does not try to solve the problems such as undo or redo, persistence, or the forms where Redux has extension points like store enhancers and middleware.

* No nice Flow integration yet: Flux allows you to do impressive static type checks that Redux does not support yet.

What do you mean by the state in ReactJs?

State of a component is an object that holds some information that may change over the lifetime of the component. We should always make our state as simple as possible and minimize the number of stateful components.

State the difference between a controlled compound and uncontrolled component?

The difference between them is:

* A controlled component is a component where React is in power and is the single source of fact for the form data.

* An uncontrolled component is where your form data is handled by the DOM, in its place of within your React component.

Why would you use force update in a React?

In order to power a re-render if there is some form, React is not detecting that requires a revision to the UI.

What are the limitations of ReactJs?

The limitations of ReactJs are:

* The code difficulty increases with inline templating and JSX.
* Too many lesser components are important to over-engineering.
* There is a knowledge curve for beginners who are novel to web development.
* React is just an outlook library, not a full-blown framework.

How Redux Works - Redux Workflow

* Redux allows you to manage the state of the application using single source of truth, called Store, Any * Component can directly access the state from the Store using Subscribe method.

Let's understand the Redux workflow step by step:

* Store - Redux offers a solution of storing all your application's state at one place, called store.
* Action - Actions can be dispatch based on the Event (e.g. OnClick, OnChange, etc).
* Reducer - Reducers are the pure functions which takes the previous state and an action, and return the next state. (Always return new state objects, instead of mutating the previous state).
* Subscribe - Any components can easily subscribe to store.
In Redux, components don't communicate directly with each other, but rather all state changes must go through the single source of truth, the store.

What are the benefits of using Redux?

Following are the benefits of using Redux:

Single-Source of Truth
Predictable States
Easy to Maintain
Reusable Code
No need to uplift State
Easy to Debug

How to structure Redux top-level directories?

All the applications have multiple top-level directories as mentioned below:

* Components: it is used for “dumb” React components that are unfamiliar with Redux.
* Containers: It is used for “smart” React components which are connected to the Redux.
* Actions: It is used for all the action creators, where the file name should be corresponding to the part of the app.
* Reducers: It is used for all the reducers where the file name is corresponding to the state key.
* Store: it is used for store initialization. This directory works best in small and mid-level size apps.

Redux workflow features?

* Reset: Allow to reset the state of the store.
* Revert: Rollback to the last committed state.
* Sweep: All disabled actions that you might have fired by mistake will be removed.
* Commit: Makes the current state the initial state.

Define the difference between state and props?

Both props and state are basic JavaScript objects. While both of them grasp information that influences the output of cause to be and they are diverse in their functionality relating to the constituent, i.e.,

* The state is managed within the element similar to variables confirmed within a purpose.

* Props get approved to the constituent similar to utility parameters.

What is store in redux?

The store holds the application state and supplies the helper methods for accessing the state.
Register listeners and dispatch actions. There is only one Store while using Redux. The store is configured via the createStorefunction. The single store represents the entire state. R
ducers return a state via action.

What is the typical flow of data in a React + Redux app?

Call-back from the UI component dispatches an action with a payload; these dispatched actions are intercepted and received by the reducers. This interception will generate a new application state. From here, the actions will be propagated down through a hierarchy of components from the Redux store. The below diagram depicts the entity structure of a redux+react setup.

What do you mean by Virtual DOM?

It is an in-recollection illustration of Real DOM. The depiction of a UI is kept in memory and synced with the “real” DOM. It’s a pace that happens among the render function being called and the displaying of basics on the screen.

Explain Flux?

It is an application design model used as a substitute for the more traditional MVC outline. It is not a framework but a new type of structural design that complements React and the notion of Unidirectional Data Flow.

What is an action in Redux?

Actions are the plain JavaScript objects which contain a type field. Action can be considered as an event that can describe something that has happened in the application.

Always remember actions should contain a small amount of information that is needed to mention what has happened.

Where can Redux be used?

Redux is majorly used in combination with reacting. It also has the ability to get used to other view libraries too. Some of the famous entities like AngularJS, Vue.js, and Meteor. It can get combined with Redux easily. This is a key reason for the popularity of Redux in its ecosystem. So many articles, tutorials, middleware, tools, and boilerplates are available.

Do you think you need to keep all components states in redux store?

Yes! You require keeping your application state as miniature as possible. You don't have to drive everything in there. Only do that makes a lot of intelligence to keep something there, or it makes your life easier when using Dev Tools.

Name some features of Redux Dev tools?

Some of the features are:

* Lets you go backside in time by “cancelling” measures.

* If the reducers toss, you will see throughout which act this happened, and what the mistake was

* Lets you examine every state and action freight.

* If you modify the reducer code, each “staged” accomplishment will be re-evaluated.

Define Redux Thunk?

It is known as middleware that permits you to mark achievement creators that revisit a function in its place of an act. The Thunk can be utilized to hold up the post of an action. The internal function receives the layup methods to transmit and get state () as parameters.

Do you need to keep all component states in the Redux store?

You do not need to push everything in the redux store as you have to keep your application state as small as possible. You should only do it if it makes a difference to you to keep something there or maybe helping you in making your life easier while using Dev Tools.

What are the core principles of Redux?

There are three core principles that Redux follows:

<> Single source of truth: The global state of your app is put away in an object tree inside a single store.

<> The state is read-only: State can only be changed by emitting an action, an object that explains what has happened.

<> Changes are made with pure functions: This is to define how the state tree is being transformed by the actions, you have to write pure reducers.

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