Javascript Interview Prep Questions (Pt-2)

Javascript Basic Questions (Part-2)

1. How do you find if a given object is an array in JS?

• We can find if a given object is an array by .isArray(). If it returns true it is an array and vice versa.
• Visually, if an object is enclosed within [], it tends to be an empty array.

function checkObject(arr) {
  // check if arr is array
  const result = Array.isArray(arr)

  if (result) {
    console.log(`[${arr}] is an array.`)
  } else {
    console.log(`${arr} is not an array.`)
  }
}

const array = [1, 2, 3]

// call the function
checkObject(array)

Output
[1,2,3] is an array.

2. What is Prop drilling and how to avoid it?

• Passing of data from one component through several connected components to the component that needs the data.
• Can be avoided by using React Context (useContext), just wrap it in fn.provider . It provides a way to pass data through multiple nested levels of components without having to manually pass that data to each level.

useContext()

• useContext is a React Hook that lets you read and subscribe to context from your component.

const value = useContext(SomeContext)

3. What is Callback hell?

• When we nest multiple callbacks within a function is called a callback hell.
• It makes the code very difficult to understand and maintain.

4. What are arrow functions?

• Arrow functions are lexically scoped.
• With arrow functions the this keyword always represents the object that defined the arrow function i.e gets this. from where it was saved.

let x = (x, y) => x * y

5. What is new keyword?

• It creates and returns objects automatically (automates).
• Creates an instance of an object by calling the constructor method.