React JS Interview Questions.

1. We can go for keys when there is possibility that our user could change the data.

• Keys
  ref
  both
  none of above

2. JSX is typesafe.

• True
  False

3. React merges the object you provide into the current state using __________.

• setState()
  State()

4. Arbitrary inputs of components are called __________.
   Keys

• Props
  Elements
  Ref

5. _________ can be done while more than one element needs to be returned from a component.
   Abstraction
   Packing
   Insulation

• Wrapping

6. Which of the following needs to be updated to achieve dynamic UI updates?

• State
  Props

7. Lifecycle methods are mainly used ___________.
   To keep track of event history
   to enhance components

• freeup resources
  none of the options

8. State can be initialized when code is loaded or state can be set on event changes.
   False

• True

9. ref is used to refer a element / component returned by _______________.
   react()

• render()
  reduce()
  refer()

10. In JSX most of the errors can be caught during _________.
    Interpretation
    Execution

• Compilation
  Build

11. Components cannot refer to other components in their output.
    True

• False

12. JSX is faster because it performs ____________ while compiling code to JavaScript
    Modification
    Compression

• Optimization
  Encryption

13. If our elements are dynamic, react can keep track of the changes using keys.

• True
  False

14. Function that does not change its results for the same set of inputs are called __________.

• Pure functions
  Impure Functions

15. What is the smallest building block of ReactJS?
    none of the options
    props

• elements
  components

16. An altered component may be uniquely identified with the help of ref.
    True

• False

17. React considers everything as _______.
    User interface
    elements

• components
  Objects

18. React keeps track of what items have changed, been added, or been removed from a list using ________.
    state
    props

• keys
  ref

19. React is mainly for building _____________.
    Database
    Connectivity

• User interface
  Design platform

20. React supports all the syntax of _________________.

• ES6
  Redux
  None of options
  Native Java

21. In React state can be accessed using ________.
    current

• state
  current()
  state()

22. How can we prevent default behavior in React?
    None of the options
    using revokeDefault()

• Using preventDefault()
  using avoidDefault()

23. Invoked once, only on the client, after rendering occurs.
    componentWillUnmount
    shouldComponentUpdate
    componentWillMount

• componentDidMount