In the fast-paced world of tech, interviews often focus on both theoretical knowledge and practical skills. Here's a cheat sheet that covers essential JavaScript concepts and coding challenges, providing both code snippets and explanations.

This guide is designed to help you swiftly review and understand common topics that you're likely to encounter during technical interviews for a developer position. It spans a range of subjects from basic programming constructs and DOM manipulation to advanced topics like asynchronous programming and error handling, equipping you with the insights to tackle front-end development questions with confidence.

1. Basic Understanding:

• What are primitive data types in JavaScript?

  • Answer: The primitive data types in JavaScript are Undefined, Null, Boolean, Number, BigInt, String, and Symbol.

• How do you define variables?

  var x = 10;
  let y = 20;
  const z = 30;

• Answer: Variables can be defined using the var, let, or const keywords. var is function-scoped, let and const are block-scoped. const is used for variables whose values should not be reassigned after their initial assignment.

• Can you explain the difference between let, const, and var?

  var x = 10;  // function-scoped, re-assignable
  let y = 20;  // block-scoped, re-assignable
  const z = 30;  // block-scoped, not re-assignable

• Answer: var is function-scoped and can be reassigned. let and const are block-scoped. let can be reassigned while const cannot be reassigned after the initial assignment.

2. Functions and Scope:

• How do you declare a function?
  • Answer: Functions are declared using the function keyword, followed by the function name, parameters within parentheses, and the function body within curly braces.

  function myFunction(parameters) {
    // function body
  }

• What is the difference between function expressions and function declarations?
  • Answer: Function declarations are hoisted to the top of their scope with the function body, allowing them to be used before they're defined. Function expressions are not hoisted, and can only be used after they're defined. The variable holding the function expression is hoisted but assigned undefined initially.

  // Function Expression:
  const myFunction = function(parameters) {
    // function body
  };

  // Function Declaration:
  function myFunction(parameters) {
    // function body
  }