ECMAScript 6

Question 1

object = { ‘name’ : ‘Frank’, ‘age’ : 34 };

Show how to destructure the object into
var x, y;

Answer 1

( { name : x, age : y } = object );

Question 2

What is the scoping of Var declared outside a function

Answer 2

Global

Question 3

Object Destructuring
object = { ‘name’ : ‘Frank’, ‘age’ : 34 };

Show how to destructure the object into
var name, age;

Answer 3

[ name, age ] = object;

Question 4

let b = 1;
function () {
    let b = 2;
};
   What is b = ?

Answer 4

1

Question 5

Show an example of a computed property name in an object.

Answer 5

object = {
[ “first” + “name”] : ‘Luther’
};

Question 6

What does the ‘spread’ operator do?

Answer 6

It takes and array (list) and 'spreads' out the contents as if they were individual values applied separately.
function threeParms(a, b, c) ...
as in:
var list = [ 10, 20, 26 ];
threeParam(...list);

Question 7

Show the ES6 way to define a function within an object.

Answer 7

let object = {
       myFunction() {
           console.log('hello world');
           } 
      }
object.myFunction();

Question 8

What about const objects:
const boss = { 'firstname': 'Chuck', 'lastname': 'Duncan' };
...
boss.firstname = 'Pat';

Is this valid?

Answer 8

Yes, because the constant has an object assigned to it and that hasn’t changed. What changed was the contents of the object. That is legal.

Question 9

Can a LET variable be reassigned?

as in Let a = 5; Let a = 10;

Answer 9

No it will throw an exception.

Question 10

What is the scope of a var inside a function

Answer 10

Just the function contents

Question 11

What is the scoping of Let

Answer 11

Block scoping

Question 12

What is the scoping rule for ‘const’?

Answer 12

Block scoped

Question 13

function myFn( { ‘name’ = ‘Chuck’, ‘age’ = 69, ‘profession’ = ‘genius’ } = { } ) { … }

myFn( { ‘name’ : ‘Pat’, ‘profession’ = ‘retired’ } );

Explain…

Answer 13

The myFn arguments effectively replace the { } and the assignment continues. If NO parameter’s are given, the { } is applied, but the parameters each have default values, which are assigned.

Question 14

What does the following produce:

var smallList = [ 'c', 'd', 'e' ];
var result = [ 'a', 'b', ...smallList, 'f', 'g' ]

Answer 14

result = [ ‘a’, ‘b’, ‘c’, ‘d’, ‘e’, ‘f’, ‘g’ ]

Question 15

Where is the ‘rest’ operator used?

Answer 15

In declaring a function; it embodies the ‘rest’ of the parameters that may have optionally been supplied:

function trafficTypes( lane, speed, …other );

Question 16

[ a, b, c] = [ 1, 2, 3]

How can this be rewritten to NOT assign the ‘2’ to any variable.

Answer 16

[ a, , c] = [ 1, 2, 3]

Question 17

Given myArray = [ 1, 2, 3, 5, 8 ];
And var= a, b, c, d, e;

Show how to “destructure” the values in the myArray into the vars.

Answer 17

[ a, b, c, d, e ] = myArray;

Likewise:
[ a, b, c, d, e ] = [ 1, 2, 3, 5, 8 ];

Question 18

What delineates block scoping

Answer 18

{ }

Question 19

var a = 1;
Function () {
   var a = 2;
}
    What is a =?

Answer 19

1, because the var in the function declares an scoped instance of a. Also, the anonymous function hasn’t been executed.

Question 20

function sample(x=1, y=2, z=3) {
...
Can a function parameter's value be an expression?

Answer 20

Yes

Question 21

Given:
   let circleArea = ( pi, r ) => { return pi * r * r ; };

Restate this in the form of an anonymous function.

Answer 21

let circleArea = function(pi, r) { return pi * r * r; };

Question 22

Can a var variable be reassigned

Answer 22

Yes

Question 23

Name a difference between arrow functions and traditional functions.

Answer 23

The this operator works differently and an arrow function cannot be new-ed.

Question 24

Object Destructuring

object = { ‘name’ : ‘Frank’, ‘age’ : 34 };

Show how to destruction object into
var name, age;

Answer 24

[name, age ] = object ;

Question 25

In ES5:
var x = 1, y = 2;
var object = { x : x, y : y };

Rewrite this in ES6

Answer 25

let x = 1, y = 2;
let object = { x, y };