Top 5 Basic React JS Interview Questions and Answers

1. What is a state?

• It is an object that holds some information that may change over the lifetime of the component
• Try to make the state as simple as possible and minimize the number of stateful components
• state is similar to props, except it is private and fully controlled by the component
• state is not accessible to any component other than the one that owns and sets it

2. What are props?

• props are inputs to components
• They are single values or objects containing a set of values that are passed to components on creation
• They are data passed down from a parent component to a child component

3. What is the difference between state and props?

• Both props and state are plain Javascript objects
• Both hold information that influences the output of render
• Difference: props get passed to the component, state is managed within the component

4. What is Virtual DOM?

• It is an in-memory representation of a Real DOM
• It is kept in memory and synced with the “real” DOM
• It’s a step that happens between the render function being called and the displaying of elements on the screen
• The entire process is called reconciliation