JavaScript - Basic

Question 1

pop() Method

Answer 1

remove the last element of an array

Example:
var fruits = [“Banana”, “Orange”, “Apple”, “Mango”];
fruits.pop();

Result:
Banana,Orange,Apple

Question 2

push() Method

Answer 2

Add a new item to the end of an array

Example:
var fruits = [“Banana”, “Orange”, “Apple”, “Mango”];
fruits.push(“Kiwi”);

Result:
Banana,Orange,Apple,Mango,Kiwi

Question 3

join() Method

Answer 3

Joins the element of an array into a string

Example:
var fruits = ["Banana", "Orange", "Apple", "Mango"];
var energy = fruits.join();

Result:
Banana,Orange,Apple,Mango

Question 4

reverse() Method

Answer 4

Reverse the order of the elements in an array

Example:
var fruits = [“Banana”, “Orange”, “Apple”, “Mango”];
fruits.reverse();

Result:
Mango,Apple,Orange,Banana

Question 5

split() Method

Answer 5

Splits string into an array of substrings

Example:
var str = "How are you doing today?";
var res = str.split(" ");

Result:
How,are,you,doing,today?

Question 6

round() Method

Answer 6

Math.round(x) (aka round() Method)

Example:
Math.round(2.5);

Result:
3

Question 7

parseInt() Function

Answer 7

The parseInt() function parses a string and returns an integer.

Example:

a) var c = parseInt(“10.33”) + “<br></br>”;
b) var d = parseInt(“34 45 66”) + “<br></br>”;

Result:
10
34

Question 8

n!

Answer 8

Factorial. An example is:

5! = 1 * 2 * 3 * 4 * 5 = 120

function factorialize(num) {
  var factorial = 1;
  for (var i = 2; i

Question 9

String.replace() Method

Answer 9

Return a string where “Microsoft” is replaced with “W3Schools”:

var str = "Visit Microsoft!";
var res = str.replace("Microsoft", "W3Schools");

The result of res will be:

Visit W3Schools!

Question 10

String.toLowerCase() Method

Answer 10

Convert the string to lowercase letters:

var str = "Hello World!";
var res = str.toLowerCase();

The result of res will be:

hello world!

Question 11

String slice() Method

Answer 11

Extract parts of a string:

var str = "Hello world!";
var res = str.slice(1,5);

The result of res will be:

ello

Question 12

RegExp Object

Answer 12

A regular expression is an object that describes a pattern of characters.

Regular expressions are used to perform pattern-matching and “search-and-replace” functions on text.

http://www.w3schools.com/jsref/jsref_obj_regexp.asp

Question 13

switch statement

Answer 13

[JS Control Flow] Switch allows you to preset a number of options (called cases), then check an expression to see if it matches any of them.

switch (/*Some expression*/) {
    case 'option1':
        // Do something
        break;
    case 'option2':
        // Do something else
        break;
    case 'option3':
        // Do a third thing
        break;
    default:
       // Do yet another thing
}

Question 14

What will the following expression return:

true && false;

Answer 14

False

true && true; // => true
true && false; // => false
false && true; // => false
false && false; // => false

Question 15

What will the following expression return:

false || true;

Answer 15

True

true || true; // => true
true || false; // => true
false || true; // => true
false || false; // => false

Question 16

What will the following expression return:

!false; // => true

Answer 16

True

!true; // => false
!false; // => true

Question 17

Create an array called ‘list’ with 3 items in it.

Answer 17

var list = [“errands”, “cleaning”, “homework”];

Question 18

Write the code to log to the console each item of the following array:

var languages = [“HTML”, “CSS”, “JavaScript”, “Python”, “Ruby”];

Answer 18

for (var i = 0; i

Question 19

What is a heterogeneous array?

Answer 19

An array that contains a mixture of data types like:

var mix = [42, true, “towel”];

Question 20

What is a two-dimensional array?

Answer 20

An array inside an array, in this case an array nested one layer deep:

var twoDimensional = [[1, 1], [1, 1]];

Question 21

What is a jagged array?

Answer 21

An array that includes arrays of different lengths e.g.

var jagged = [[“name”, “gender”, 30], [“name”, “gender”], 33, true];

Question 22

Write an example of object literal notation by creating the object “me” and giving it two keys.

Answer 22

var me = {
  name: "bubba",
  age: 31
}

Question 23

Create a new object called “myObj” using the object constructor. Then, assign a name to myObj using the shorthand version.

Answer 23

var myObj = new Object();

myObj.name = “Bubba”;

Question 24

for key in object

Answer 24

for key in object describes the iteration through all the keys of an object. Because this is not sequentially indexed, in is the control. Objects generally have a finite number of properties in them, and this loop susses them out, one at a time.

Question 25

Create an object called “friends” and create two objects inside of that named “bill” and “steve”.

Each friend will need a first name, last name, number and address.

Make sure the address is an array.

Answer 25

var friends = {
    bill: {
        firstName: 'bill',
        lastName: 'smith',
        number: '111-111-1111',
        address: ['One Apple Drive', 'Cupertino', 'CA', '12345']
    },
    steve: {
        firstName: 'steve',
        lastName: 'ferguson',
        number: '22-222-2222',
        address: ['One Facebook Way', 'Palo Alto', 'CA', '54321']
    }
};

Question 26

Create a function that will print out all entries in an object called “friends”.

Answer 26

var list = function(friends) {
    for (var i in friends) {
        console.log(i);
    }
}

Question 27

What is a for/in loop look like and what does it do?

Answer 27

for (var key in object) {
  // Access that key's value
  // with object[key]
}

*the “key” bit can be any placeholder name you like. It’s sort of like when you put a placeholder parameter name in a function that takes arguments.

Question 28

Definite Object Methods

Answer 28

Object methods are actions that can be performed on objects.

Object properties can be both primitive values, other objects, and functions.

An object method is an object property containing a function definition

Question 29

const

Answer 29

ES6. const means that the variable can’t be reassigned.

In other words, const is a signal that the variable won’t be reassigned.

Question 30

let

Answer 30

ES6. let, is a signal that the variable may be reassigned, such as a counter in a loop, or a value swap in an algorithm.

It also signals that the variable will be used only in the block it’s defined in, which is not always the entire containing function.