Javascript

Question 1

Write:

How to include a javascript file?

Question 2

Is JS a dynamic language?

If so, what does that entail?

Answer 2

It is a dynamic language. As such, the value of the variables can be modified at runtime

Question 3

What are the three ways to declare variables?

Answer 3

let, var and const

Question 4

What happens if a variable is created without being declared?

Answer 4

They are global

Question 5

What happened if a variable is not assigned a value?

Answer 5

Its value is “undefined”

Question 6

What is a Falsy value?

What are the falsy values?

Answer 6

A value that is not false, but would be false in a Boolean context

undefined, NaN, null, “”, 0

Question 7

What happens if we try to + a string and a number?

Answer 7

The number is coerced to a string.

Question 8

What are the five primitive data types in JS?

Answer 8

Number, String, Boolean, null and undefined

Question 9

What are the comparison rules for < and >

Answer 9

1-If one is a number and the other can be converted: comparison
2-If one is a number and the other one cannot be converted: false
3-If both are strings: string comparison

Question 10

What are the comparison rules for all the other operators (asterisk, /, %)

Answer 10

If one cannot be converted to a number: NaN

Question 11

What are the two types of equality operators, and how do they differ?

Answer 11

The loose equality (==, !=) and the strict equality (===, !==). The former does type coercion, the latter does not

Question 12

For the variable declarator “let”, tell us about its scope, whether it can be redeclared and whether a value must be declared at creation.

Answer 12

Block scope, cannot be redeclared and does not have to be assigned a value at declaration

Question 13

For the variable declarator “const”, tell us about its scope, whether it can be redeclared and whether a value must be declared at creation.

Answer 13

Block scope, cannot be redeclared and must be assigned a value at declaration

Question 14

For the variable declarator “var”, tell us about its scope, whether it can be redeclared and whether a value must be declared at creation.

Answer 14

Global scope, can be redeclared and can also be declared before use

Question 15

How to traverse all properties in an object?

Answer 15

for (x in object){…}

Question 16

How to create an object?

Answer 16

var object = new Object();

Question 17

Write

What are the two ways to create properties in an object?

Answer 17

either myobj.prop1=… or var myobj={prop1: …, prop2:…};

Question 18

Write

What are the two ways to create arrays?

Answer 18

var myArray = [1, 2, 3]
var myArray = new Array(1,2,”3”)

Question 19

What does .join do on an Array?

Answer 19

Array.join(“;”) for example, separates all the elements of the array by ; and returns it

Question 20

What does Array.toString() do?

Answer 20

It concatenates the array and separates it with commas (like .join(“,”) would)

Question 21

What does .slice() do?

Answer 21

It cuts a part of the array, from the first integer (inclusive) to the second integer (exclusive)

Question 22

What is the difference between actual parameters and formal parameters?

Answer 22

Formal parameters are those written in the function creation while actual parameters are those used in the function call

Question 23

Write

A sorting function to sort numbers, as well as its call

Answer 23

function sortNumber(a,b){
return a-b;
}
document.write(array.sort(sortNumber));

Question 24

Write

How to write an anonymous function?

Answer 24

var f = function (a,b) {return a-b};

Question 25

What happens if the prototype of an object is modified?

Answer 25

It changes the template of all objects of this type

Question 26

Write

A constructor for a car object and the subsequent creation of a car object.

Answer 26

function car(make, year, model) {
this.make=make;
this.year=year;
this.model=model;
}

let car1 = new car(“Ford”, “2017”, “Fiesta”);

Question 27

Write

For the car constructor, write a display function and add it to the constructor

Answer 27

function displayCar(){
document.write(“Year: “+this.year);}

this.display=displayCar; (to add to the constructor, since functions can be passed as parameters)