Interview Questions.

• Explain event delegation.

• Explain how this works in JavaScript.

• Can you give an example of one of the ways that working with this has changed in ES6?

• Explain how prototypal inheritance works.

• What's the difference between a variable that is: null, undefined or undeclared?

  • How would you go about checking for any of these states?

• What is a closure, and how/why would you use one?

• What language constructions do you use for iterating over object properties and array items?

• Can you describe the main difference between the Array.forEach() loop and Array.map() methods and why you would pick one versus the other?

• What's a typical use case for anonymous functions?

• What's the difference between host objects and native objects?

• Explain the difference between: function Person(){}, var person = Person(), and var person = new Person()?

• Explain the differences on the usage of foo between function foo() {} and var foo = function() {}

• Can you explain what Function.call and Function.apply do? What's the notable difference between the two?

• Explain Function.prototype.bind.

• What's the difference between feature detection, feature inference, and using the UA string?

• Explain "hoisting".

• Describe event bubbling.

• Describe event capturing.

• What's the difference between an "attribute" and a "property"?

• What are the pros and cons of extending built-in JavaScript objects?

• What is the difference between == and ===?

• Explain the same-origin policy with regards to JavaScript.

• Why is it called a Ternary operator, what does the word "Ternary" indicate?

• What is strict mode? What are some of the advantages/disadvantages of using it?

• What are some of the advantages/disadvantages of writing JavaScript code in a language that compiles to JavaScript?

• What tools and techniques do you use debugging JavaScript code?

• Explain the difference between mutable and immutable objects.

  • What is an example of an immutable object in JavaScript?

  • What are the pros and cons of immutability?

  • How can you achieve immutability in your own code?

• Explain the difference between synchronous and asynchronous functions.

• What is event loop?

  • What is the difference between call stack and task queue?

• What are the differences between variables created using let, var or const?

• What are the differences between ES6 class and ES5 function constructors?

• Can you offer a use case for the new arrow => function syntax? How does this new syntax differ from other functions?

• What advantage is there for using the arrow syntax for a method in a constructor?

• What is the definition of a higher-order function?

• Can you give an example for destructuring an object or an array?

• Can you give an example of generating a string with ES6 Template Literals?

• Can you give an example of a curry function and why this syntax offers an advantage?

• What are the benefits of using spread syntax and how is it different from rest syntax?

• How can you share code between files?

• Why you might want to create static class members?

• What is the difference between while and do-while loops in JavaScript?

• What is a promise? Where and how would you use promise?

Coding questions

• Make this work:

duplicate([1,2,3,4,5]); // [1,2,3,4,5,1,2,3,4,5]

• Create a for loop that iterates up to 100 while outputting "fizz" at multiples of 3, "buzz" at multiples of 5 and "fizzbuzz" at multiples of 3 and 5

• What will be returned by each of these?

console.log("hello" || "world")
console.log("foo" && "bar")

• Write an immediately invoked function expression (IIFE)