Typescript 102 // Data & Variables

Question 1

What is a variable?

Answer 1

Variable Definition: A variable is a user-defined storage of data

Question 2

What is a variable declaration/initialisation?

Answer 2

A variable must be declared before using in a program. Declaration is stating the variable name with the keyword, essentially reserving the memory space. Initialisation is giving that declared variable a value.

Question 3

What is good practice for declaring variables that have no value?

Answer 3

Initialise to 0 or Null

Question 4

What are the 3 keywords used to declare variables

Answer 4

let, const, var

Question 5

What is the initialisation syntax for a LET declaration?

Answer 5

let var_name = value;
(e.g. let num1 = 5; )

Question 6

How many times can you declare the same variable with the keyword LET?

Answer 6

Once only; the let declaration does not allow for redeclaration, only changing the value stored. In other words, there is no need to use let when changing values.
(e.g. let num1 = 5;
num1 = 6;

Question 7

What is the characteristic of a variable declared with const (as opposed to let or var)?

Answer 7

It is constant and cannot be reassigned.

Question 8

Which variable declaration keywords allow for reassigning variables to new values?

Answer 8

let & var.

const reassignment is invalid.

Question 9

What is the declaration syntax for a CONST declaration?

Answer 9

const var_name = value;
(e.g. const num1 = 5; )

Question 10

Why is initialisation essential when declaring using const?

Answer 10

It is not possible to reassign the variable when using const, so the first declaration must contain the data value it is assigned to.

Question 11

What is the similarity between LET and VAR variable declarations

Answer 11

They store the variable as a modifiable value.

Question 12

What is the declaration syntax for a var declaration?

Answer 12

var var_name = value;
(e.g. var num1 = 5; )

Question 13

Why is let generally preferable to var?

Answer 13

Compiler errors: If something has gone wrong the compiler will show up, meaning problems can be more easily caught

Linearity: let variables cannot be used before declaration, which encourages linearity in the code

Single Declaration: Makes it less likely for accidental reassignment errors.

Question 14

Typescript has the ability to add static typing to variable declarations. What is static typing?

Answer 14

Static typing is the ability to make a variable always of the same type, meaning if the wrong data type is used there will be a compiler error.

Question 15

What is the typescript static typing initialisation Syntax?

Answer 15

let var_name:datatype = value;
const var_name:datatype = value;
var var_name:datatype = value;
(e.g. let num1:number = 5;)

Question 16

What are the valid characters for variable names

Answer 16

Letters, Underscores and Numbers.

NUMBERS NOT VALID AT THE START)

Question 17

What are the primary data types in Javascript/Typescript?

Answer 17

Number, string, boolean, valueless.

Question 18

What is the difference between Typescript and Javascript Type Inference styles.

Answer 18

After initialisation, Javascript allows for reassigning data type of variable.
Typescript does not allow for reassignment of data type, regardless of type static typing specified.

Question 19

In typescript declarations, what does the colon mean?

Answer 19

“of the type”.