Intro to JavaScript

Question 1

What does it mean to declare a variable?

Answer 1

Tell the JavaScript engine that there exists a variable with a given name.

Question 2

What does it mean to initialize a variable?

Answer 2

Tell the JavaScript engine that there exists a variable with a given name that will have an initial value defined by the code to the right of the assignment operator.

Question 3

What does it mean to declare a function?

Answer 3

Tell the JavaScript engine what a function is named, what parameters can be passed in, what the function does then returns.

Question 4

What types of data can be stored in a variable?

Answer 4

String, Number (Integers and Real/Decimal), Boolean (true/false), Objects, Functions

Question 5

How is a date stored internally by the JavaScript engine?

Answer 5

As a real number (decimal) that represents the seconds since January 1, 1970. Left of the decimal represents whole seconds, and to the right of the decimal represents the fraction of the second.

Question 6

What is a JavaScript engine?

Answer 6

The program that runs JavaScript in the browser

Question 7

TRUE or FALSE: an array is an object?

Answer 7

TRUE. Arrays are special types of objects in JavaScript that have some special syntax. But normal object syntax applies as well. For example, you can declare an array with 
var array = [];
or with
var array = new Array();

Question 8

What does null mean?

Answer 8

A value is explicitly not provided

Question 9

What does undefined mean?

Answer 9

A value has not been defined

Question 10

What is the difference between null and undefined?

Answer 10

null values do not exist, but are purposely set as not existing, while undefined values are simply unset to any value, including null.

Question 11

What does NaN mean?

Answer 11

Not a NumberExamples would be 100/0 or sqrt(-1)

Question 12

What “Truthy / Falsey”?

Answer 12

It is a way to evaluate conditions whereby a list of FALSE values is established and every other value is considered to be TRUE.

Question 13

TRUE or FALSE: a variable can be changed from a string to a number in the middle of a program?

Answer 13

TRUE. Variables can be set using the assignment operator at any time in the program, and they can be set to any valid type with no limit on how many times the assignment can be performed.

Question 14

What is the assignment operator?

Answer 14

=

Question 15

What is the assignment operator in the context of a property of an object?

Answer 15

:

Question 16

TRUE or FALSE: a function can be stored in a variable?

Answer 16

TRUE

Question 17

How would you initialize and then call a function that is stored in a variable?

Answer 17

var nameOfFunction = function(stringParam1, numberParam2, objectParam3) {
 return;
}

nameOfFunction(“something”, 2763.98, {
 stringProp1: “some value”,
 numberProp2: 27626
});

Question 18

TRUE or FALSE: functions need to be defined before they are used?

Answer 18

FALSE. Functions can be defined anywhere

Question 19

TRUE or FALSE: functions that are stored in variables need to be defined before they are used?

Answer 19

TRUE. This is like all variables. Variables must be declared before being referenced.

Question 20

How would one describe the following line of code:

var totalPrice = itemPrice * (1 + taxRate);

Answer 20

Store the product of the itemPrice and the quantity of one added to the taxRate in the totalPrice variable.

Question 21

How is the assignment variable processed?

Answer 21

Run the code on the right of the assignment variable, then store the result into the variable, constant or property on the left side.

Question 22

TRUE or FALSE: if a function has 3 parameters, you are required to pass in 3 parameters?

Answer 22

FALSE. Functions can have any number of parameters. Any parameters that do not have values passed in are set to null.

Question 23

How would you declare and then call a function with 3 parameters, passing in values to the first two parameters when called?

Answer 23

nameOfFunction(“value1”, 827); 

function nameOfFunction(stringParam1, numberParam2, objectParam3) {
 return;
}

Question 24

TRUE or FALSE: it doesn’t matter if a variable is declared as all lower case, you can reference the variable with capital letters too, so long as it is the same letter.

Answer 24

FALSE. Variables and functions are case sensitive, which means that the exact letters that are used to name the variable or function must be used to reference it. 

console.log is not the same as console.Log

Question 25

How do you declare an empty array?

Answer 25

var array = [];
or with
var array = new Array();

Question 26

How do you declare a date variable?

Answer 26

var now = new Date();

Question 27

How do you declare make an object that can be used with the new keyword?

Answer 27

The object must be declared as a function with it’s initial properties passed in as parameters, then set using the this keyword:

function CustomObject(stringParam1, booleanParam2) {
 this.stringProp1 = stringParam1;
 this.booleanProp2 = booleanParam2;
}

Then it can be treated like a normal object

var objectName = new CustomObject();
console.log(“object prop1”, objectName.stringProp1);

Question 28

How do you declare a simple object?

Answer 28

var objectName = {
 stringProp1 : “”,
 booleanProp2: false,
 numberProp3: 0.0,
 functionProp4: function(param1) {
 return param1;
 }
}

Question 29

Give an example of how to declare then initialize a variable to an empty string

Answer 29

var name = “”;

Question 30

What is the meaning of the character ;

Answer 30

Execute the code to the left (end of line)

Question 31

What is a compound condition?

Answer 31

A condition that has multiple statements that can be evaluated that are joined by && (AND) or || (OR)

Question 32

When expressions are evaluated in an if or else if statement, or in a boolean variable, how are they processed?

Answer 32

Compound conditions are processed left to right. Each statement is evaluated, starting with the left most statement, until a true statement is found. Remaining statements are ignored. If all statements are false, they are all executed.

Question 33

What is the name of the object populated by the browser’s JavaScript engine automatically that represents the HTML document itself?

Answer 33

document