Infosys Interview Question

For JavaScript; what is a variable? What is Let and Const? What are the different data structures? What are the different data types? What would 6+1+ “7” be? What is an object? What is the difference between == and ===? What is isNaN() and what does it return? Oops - what is inheritance? what is abstraction? What is super()? What is a constructor function?