1. JavaScript Fundamentals

• Question: What are variables in JavaScript and what are the differences between var, let, and const?

  • Variables: Containers that store data. You can declare a variable and assign values to it for use in your code.
  • var x let x const
    • var
      • Function scope: If declared inside a function, it can be accessed anywhere within that function.
      • Can be redeclared, which may lead to unexpected behavior.
    • let
      • Block scope: Within a function, it can only be accessed if within the same block { }.
      • Cannot be redeclared (i.e., declaring the same variable again).
      • Can reassign a value to the variable.
    • const
      • Block scope: Within a function, it can only be accessed if within the same block { }.
      • Cannot be redeclared.
      • Cannot reassign a value, except if it is an array or object (properties and elements can be modified).

  Note: In var, let, and const, a variable declared inside a function can only be accessed within that function. However, with var, it does not need to be within the same code block {}.
  

  function testVar() {
    if (true) {
      var x = 10;  // var is visible throughout the function
    }
    console.log(x);  // Works and prints 10
  }
  
  function testLet() {
    if (true) {
      let y = 20;  // let is only visible within the block {}
    }
    console.log(y);  // Error! y is not available outside the block {}
  }
  
  testVar();  // Works and prints 10
  testLet();  // Causes an error
  

• Question: How do functions work in JavaScript? What is the difference between a regular function and an arrow function?

  • Functions: Are blocks of code designed to perform tasks. They can be called from different parts of the code to avoid repetition and ensure better organization.