JavaScript - Code Academy

Question 1

Access a single dimensional array element

Answer 1

array[index]

Question 2

Create a single dimensional array

Answer 2

var arrayName = [element1, element2, …, elementN]

var myArray = new Array(45 , “Hello World!” , true , 3.2 , undefined);

Question 3

Create a multi dimensional array

Answer 3

var arrayName = [[1, 2, 3], [1, 2, 3,], [1, 2, 3]]

Question 4

Create an array using an array constructor

Answer 4

var stuff = new Array();

stuff[0] = 1;
stuff[1] = 2;

Question 5

Access a nested array element

Answer 5

array[index][index]

Question 6

Boolean literals

Answer 6

True

False

Question 7

Boolean logical operators

Answer 7

expression1 && expression2 
//returns true if both the expressions evaluate to true

expression3 || expression4 
// return true if either one of the expression evaluates to true

!expression5 
// returns the opposite boolean value of the expression

EXAMPLES

if ( true && false )alert("Not executed!");
//because the second expression is false

if( false || true )alert("Executed!");
//because any one of the expression is true

if( !false )alert("Executed!");
// because !false evaluates to true

Question 8

Boolean comparison operators

Answer 8

x === y // returns true if two things are equal
x !== y // returns true if two things are not equal
x = y // returns true if x is greater than or equal to y
x y // returns true if x is greater than y

Question 9

Boolean - == vs. ===

Answer 9

A simple explanation would be that == does just value checking ( no type checking ) , whereas , === does both value checking and type checking .

expression == expression
expression === expression

EXAMPLES

‘1’ == 1 //true (same value)
‘1’ === 1 // false (not the same type)

Question 10

Single line comment

Answer 10

//

Question 11

Multi-line comment

Answer 11

/*

Text
text

*/

Question 12

Print text to console

Answer 12

console.log(‘text’);

Question 13

Console timer

Answer 13

This function starts a timer which is useful for tracking how long an operation takes to happen.You give each timer a unique name, and may have up to 10,000 timers running on a given page.

console.time(timerName);

Question 14

Writing a function

Answer 14

A function is a JavaScript procedure—a set of statements that performs a task or calculates a value.

function functionName(argument1, argumentN){
    statement1;
    statement2;
    statement3;
}

Question 15

Calling a function

Answer 15

functionName(argument1, argument2, …, argumentN);

greet("Anonymous");
// Hello Anonymous!

Question 16

Function hoisting

Answer 16

The two ways of declaring functions produce different results. Declaring a function one way “hoists” it to the top of the call, and makes it available before it’s actually defined.

hoistedFunction(); 
// Hello! I am defined immediately!

notHoistedFunction(); 
// ReferenceError: notHoistedFunction is not defined

function hoistedFunction () {
  console.log('Hello! I am defined immediately!');
}

var notHoistedFunction = function () {
  console.log('I am not defined immediately.');
}

Question 17

If statemetns

Answer 17

“If” statements simply state that if this condition is true , do this , else do something else ( or nothing ) . It occurs in varied forms.

if (condition1) {
  statement1;
} else if (condition2) {
  statement2;
} else {
  statement3;
}

Question 18

For loops

Answer 18

You use for loops, if you know how often you’ll loop. The most often used varName in loops is “i”.

for ([var i = startValue];[i

Question 19

While loops

Answer 19

You use while loops, if you don’t know how often you’ll loop.

while (condition) {
  // Your code here
}

EXAMPLE
var x = 0;
while (x

Question 20

Do while loops

Answer 20

You use do while loops, if you have to loop at least once, but if you don’t know how often.

do {
  // Your code here
} while (condition);

var x = 0;
do {
    console.log(x);  // Prints numbers from 0 to 4
    x++;
} while (x

Question 21

Math - Returns a random number between 0 and 1

Answer 21

Math.random();

Question 22

Math - Returns the largest number less than or equal to a number

Answer 22

Math.floor(expression)

Question 23

Math - Returns base raised to exponent

Answer 23

Math.pow(base, exponent)

Question 24

Math - Returns smallest integer greater than or equal to a number

Answer 24

Math.ceil(expression)

Question 25

Math - Returns square root of a number

Answer 25

Math.sqrt(expresssion)

Question 26

Numbers - Returns the remainder left after dividing the left hand side with the right hand side.

Answer 26

number1 % number2

Question 27

Numbers - Returns true if the given number is not a number, else returns false.

Answer 27

isNaN([value])

Question 28

Numbers - prefix and post fix increment/decrement

Answer 28

–variable //Prefix Decrement
++variable //Prefix Increment
variable– //Postfix Decrement
variable++ //Postfix Increment

Question 29

Object literal

Answer 29

{
"property 1" : value1;
property2 : value2;
number: value3;
}

EXAMPLE
var obj = {
  name: "Bob",
  married: true,
  "mother's name": "Alice",
  "year of birth": 1987,
  getAge: function () {
    return 2012 - obj["year of birth"];
  },
  1: 'one'
};

Question 30

Property access

Answer 30

name1[string]
name2.identifier

EXAMPLE
obj[‘name’]; // ‘Bob’
obj.name; // ‘Bob’
obj.getAge(); // 24

Question 31

Class

Answer 31

A class can be thought of as a template to create many objects with similar qualities. Classes are a fundamental component of object-oriented programming (OOP).

SubClass.prototype = new SuperClass();

EXAMPLE
var Lieutenant = function (age) {
  this.rank = "Lieutenant";
  this.age = age;
};

Lieutenant.prototype = new PoliceOfficer();

Lieutenant.prototype.getRank = function () {
return this.rank;
};

var John = new Lieutenant(67);

John.getJob(); // ‘Police Officer’
John.getRank(); // ‘Lieutenant’
John.retire(); // true

Question 32

Popup boxes - alerts

Answer 32

Display an alert dialog with the specified message and an OK button.

alert(message);
alert(variable_name)