quiz.md

JavaScript Quiz

1. Primitive Values

1. What's the value of b?

let a = [0, 1];
let b = a;
a.push(2);
console.log(b);

2. What's the result of the following and why?

typeof([]);

2. Functions and this

1. What's the difference between var and let? Provide an example.
2. What's the result of following invocations?

// given the following object
const me = {
  name: 'Adam',
  hello() {
    return `hello ${this.name}`;
  }
};

me.hello();

const anotherMeSaysHello = me.hello;
anotherMeSaysHello();

const anotherMeSaysHello = me.hello;
anotherMeSaysHello.call(me);

const anotherMeSaysHello = me.hello;
anotherMeSaysHello.call({name: 'Regina'});

const anotherMeSaysHello = me.hello.bind(me);
anotherMeSaysHello();

3. What's the result of running every example? Explain the difference between them.

function test () {
  console.log(test);
  var test = 5;
}
test();

function test () {
  var test = 5;
  console.log(test);
}
test();

function test () {
  console.log(test);
  let test = 5;
}
test();

4. Explain shadowing and provide code example that demonstrates its definition.

5. Provide code example of closure.

6. Fix the alert index exercise.

3. Objects and Inheritance

1. Draw the inheritance diagram of the following. Explain the result of console.log statement.

let obj1 = { a: 1 };
let obj2 = Object.create(obj1);
console.log(obj2.a) // 1

2. Draw the inheritance diagram of the following code.

class A {
    sayA() {
        console.log('A');
    }
}
class B extends A {
    sayB() {
        console.log('B');
    }
}
const a = new A();
const b = new B();

4. Async

1. Explain how event loop works.
2. Fix the following problem.
3. What's the callback hell?
4. Implement the following using callbacks and promises.

function verifyBeforeRender(successCallback) {
  // make 2 ajax calls at the same time
  // when both of them return result, make a 3rd ajax call
  // if the result if 3rd ajax request was successful, call a `successCallback`
}

5. DOM API

1. Implement HTML page with a counter and two buttons of increment and decrement. Everything in JS. File of index.html should contain empty body as an initial state.