Javascript

Question 1

<p>+</p>

Answer 1

<p>Returns the sum or 2 numbers or concatenates 2 strings</p>

Question 2

<p>%</p>

Answer 2

<p>Modulo Returns the remainder of the first value divided by the second</p>

Question 3

Javascript Primitive Data Types(5)

Answer 3

String, Number, Boolean, Null, Undefined

Question 4

<p>2 + "2"</p>

Answer 4

<p>Concatenation = 22</p>

Question 5

10 > 2

Answer 5

returns true

Question 6

typeof()

Answer 6

tells us what the type is typeOf(10<2) returns boolean

Question 7

Javascript Null

Answer 7

A value does not exist

Question 8

Javascript Undefined

Answer 8

The variable has yet to be defined

Question 9

Javascript prompt

Answer 9

Creates and alert box that accepts an input; var x = prompt(“what is x”);

Question 10

Random number between 0 and 5

Answer 10

var _randNum = Math.round(Math.random() * 5);

Question 11

Check if number is divisible by 3

Answer 11

if (x%3 === 0)

Question 12

Property

Answer 12

Values of an object Dog.breed breed is property; noun

Question 13

Method

Answer 13

A function that is associated with an object; verb

Question 14

object literal

Answer 14

Define and create an instance at the same time var person = {Name: “Bill”, Age: 5}

Question 15

object constructor

Answer 15

function Person (name, age) {this.name = name; this.age = age;}

Question 16

Host objects

Answer 16

Objects defined by the environment; console is a common host object used in a browser

Question 17

Core objects

Answer 17

Objects defined by Javascript examples: Math, String, Boolean, Array

Question 18

global object

Answer 18

The window is the global object when the host environment is the web; window.alert() === alert()

Question 19

Local Scope

Answer 19

Variables created inside a function can’t be accessed from outside the function. (Variables created within a function that do not use the var keyword are added to global scope)

Question 20

Function scope

Answer 20

Every time we create a new function the scope changes

Question 21

Closure dictionary definition

Answer 21

A combination of a function bundled together (enclosed) with references to its surrounding state (the lexical environment)

Question 22

Closure laymans definition

Answer 22

A closure gives you access to an outer functions scope from an inner function. In JS closures are created every time a function is created at function creation time.

Question 23

Why are closures used

Answer 23

To give objects data privacy; variables can be manipulated in a different scope

Question 24

Closure benfites

Answer 24

Keep dataprivate;

Question 25

var output = (function(x) {
  delete x;
  return x;
})(0);

console.log(output);

Answer 25

Above code will output 0 as output. delete operator is used to delete a property from an object. Here x is not an object it’s local variable. delete operator doesn’t affect local variable.

Question 26

What is “closure” in javascript? Provide an example?

Answer 26

A closure is a function defined inside another function (called parent function) and has access to the variable which is declared and defined in parent function scope.

Question 27

difference between let and var

Answer 27

var is scoped to the nearest function block; let is scoped to the nearest enclosing block

Question 28

If i already have an array and i want to do the exact same operation on each of the elements in the array and return the same amount of items in the array

Answer 28

Map

Question 29

If i already have an array but i only want to have items in the array that match certain criteria

Answer 29

Filter

Question 30

If i already have an array, but i want to use the values in that array to create something completely new

Answer 30

Reduce