ES6quiz.md

ECMA Script 6 test

made by a n00b.

---

Variables declaration

const

const KEY = 'white_rabbit';
if (true) {
  const KEY = 'white_rabbit';
}
console.log(KEY);

What's the output?

white_rabbit

let

let x = 42;
if (true) {
  let x = 1337;
}
console.log(x);

What's the output?

42

let x = 42;
if (true) {
  console.log(x);
  let x = 1337;
}

What's the output?

ERROR!!!!!!

Function

// Here is a new way to define functions
var double = i => i*2;

// Which is like
var double = function (i) {
  return i * 2;
};

How to use the new syntax to define a function which doesn't take any parameter?

() => this.whatever;

Templates

var x = `foo ${y}`,
    y = `bar ${x}`;

console(x);

What's the output?

foo undefined

var x = `foo ${y}`,
    y = `bar ${x}`;

console(y);

What's the output?

bar foo undefined

Map and Set

What's the attribute to get the quantity of object stored in a Set object?

• length
• size
• weight
• area

size

What's the difference between Map/Set and MapWeak/SetWeak ?

Values cannot be primitive types. Values are objects and are "weakly" held

Declare

let options = {
  protocol: protocol,
  url: url,
  method: method,
  callback: callback
};

In ES6, is there a better way to create this object?

Class

• get
• private
• static
• constructor
• set

Which keywork is not allowed in ES6 Class definition?

Private

// Create a logger facade
class Logger {
  constructor (type = "Info") {
    this.type = type;
  }

  static create(type) {
    return new this(type);
  }

  get current() {
    return `Logger: ${this.type}`;
  }

  set current(type) {
    this.type = type;
  }

  log (message) {
    // Basic method
  }
}

Class example

Syntax

Is it legal or not?

var score = [12, 7, 14];
Math.max(...score);

Yes

function stuff(x::Number, y::String) {
  // Do stuff..
}

Nope.

function stuff(x, ...y) {
  // Do stuff..
}

Yes

function stuff(x, y=12) {
  // Do stuff..
}
stuff(2);

Yes

function stuff(x, y=x/3) {
  // Do stuff..
}
stuff(6);

Yes

var {foo, bar} = {
  foo: 'FOO',
  bar: 'BAR'
};

Yes

var [first, , last] = [1,2,3];

Yes

function stuff(a, x=12, y=42) {
  // Do stuff..
}
stuff(1, ,2);

Nope.

General

• typeof
• continue
• for..in

Which one of this keywords won't be compatible on ES6?

NONE! ES6 is completely retrocompatible

Nerd

a = 0x1101010110111;
b = 0o1101010110111;
c = 0b1101010110111;
d = 001101010110111;
e = 0E1101010110111;

Which var got the max value?

A