Chapter 2: Basic Javascript Instructions

Question 1

Statements

Answer 1

An individual instruction or step in javascript. Ends with a semi colon

var today = new Date();

Question 2

Comments

Answer 2

Used to explain code. You can have multi line using syntax /* */ or single line using // syntax . Any script surrounded by a comment is not processed by the js interpreter

Question 3

Is Javascript a case sensitive language?

Answer 3

Yes. hournow and hourNow would be treated as two different items

Question 4

code block

Answer 4

lines of code surrounded by curly braces { } do not end in a semi colon

Question 5

Variable

Answer 5

variables are used to store bits of information. If you need to reuse a piece of information you’re best to store it in a variable. Programmers say you declare a variable. You can then assign it a value. Variables stand in for a value, so rather than saying the specific number it represents (which may change), its use whatever is stored in this item instead

var dinosaur = “Spinosaurus”;

Question 6

=

Answer 6

This is the assignment operator. it assigns a value to a variable.

Question 7

undefined

Answer 7

Until a variable has a value its undefined

Question 8

Data types

Answer 8

Javascript variables can have a range of types.
numeric (e.g. 2, 0.75)
String (“Used for text)
Boolean (results in a true or false value)

There’s also arrays, objects, undefined and null

Question 9

Quote marks

Answer 9

Used to mark out strings. You can use single or double but they must match i.e. don’t start with string ‘ and end with “

Question 10

escaping quotes

Answer 10

Used when you want to show quote marks inside a string.

You can either use a backslash before a quote mark or Start the string with double quotes and then use single quotes inside the string

Question 11

Booleans are useful…

Answer 11

1. When a value can only be true or false

2. When code can take more than a single path (allows us to test if a condition/s are true or false)

Question 12

Rules for naming variables

Answer 12

1. must begin with a letter, dollar sign or underscore
2. names can contain letters, numbers, $ or an underscore
3. You cannot use keywords/reserved words
4. case sensitive
5. use a name that describes the info that the variable stores
6. camelcase

Question 13

Array

Answer 13

Arrays store a list of values or related values. The values are indexed by a number starting at 0.

Using an array is useful instead of creating individual variables when you are unsure of the number of items

var colours = [‘white’, ‘black’, ‘red’];

Question 14

array literal syntax vs array constructor sytax

Answer 14

literal:
var colours = ['white', 'black', 'red'];

constructor:
var colours = new Array ('white', 'black', 'red');

Question 15

Access values in an array

Answer 15

by index number

var colours = [‘white’, ‘black’, ‘red’];

colours[2];

by item

var colours = [‘white’, ‘black’, ‘red’];

colours.item(1);

Question 16

What does array.length do?

Answer 16

Returns how many items are in the array

Question 17

What is an expression?

Answer 17

An expression evaluates to a single value.

we can either assign a value

or

write an expression that uses two or more values to return a single value

Question 18

What is an operator

Answer 18

It’s a tool that allows us to combine multiple values into a single value.

Assignment, Aritmatic, String (+ this combines strings and numbers together concatenates)

Question 19

What is the % modulus operator

Answer 19

When doing division it returns the remainder

Question 20

When would I get NAN?

Answer 20

If you used artistic operators with values or variables and the result would not return a number