Variables

Question 1

What are the two new javascript keywords that create or declare variables?

Answer 1

let and const

Question 2

Prior to the ES6, programmers could only use the ….. keyword to declare variables.

Answer 2

var

Question 3

var myName = ‘Arya’;
console.log(myName);
// Output: Arya

1. var, short for variable, is a JavaScript keyword that creates, or declares, a new variable.
2. myName is the variable’s name. Capitalizing in this way is a standard convention in JavaScript called camel casing. In camel casing you group words into one, the first word is lowercase, then every word that follows will have its first letter uppercased. (e.g. camelCaseEverything).!!!!!!!!!!!!!!!!

Answer 3

3. = is the assignment operator. It assigns the value (‘Arya’) to the variable (myName).
4. ‘Arya’ is the value assigned (=) to the variable myName. You can also say that the myName variable is initialized with a value of ‘Arya’.
5. After the variable is declared, the string value ‘Arya’ is printed to the console by referencing the variable name: console.log(myName).

Question 4

There are a few general rules for naming variables:

Answer 4

Variable names cannot start with numbers.

Variable names are case sensitive, so myName and myname would be different variables. It is bad practice to create two variables that have the same name using different cases.

Variable names cannot be the same as keywords.

Question 5

The let keyword signals that the variable can be reassigned a different value. Take a look at the example:

let meal = ‘Enchiladas’;
console.log(meal); // Output: Enchiladas
meal = ‘Burrito’;
console.log(meal); // Output: Burrito

Answer 5

Another concept that we should be aware of when using let (and even var) is that we can declare a variable without assigning the variable a value. In such a case, the variable will be automatically initialized with a value of undefined:

let price;
console.log(price); // Output: undefined
price = 350;
console.log(price); // Output: 350

Question 6

The way you declare a const variable and assign a value to it follows the same structure as let and var.

Answer 6

However, a const variable cannot be reassigned because it is constant. If you try to reassign a const variable, you’ll get a TypeError.

Constant variables must be assigned a value when declared. If you try to declare a const variable without a value, you’ll get a SyntaxError.

Question 7

let w = 4;
w += 1;

console.log(w); // Output: 5

Can be written as w = w + 1

Mathematical Assignment Operators

+= -= *= /=

Answer 7

let x = 20;
x -= 5; // Can be written as x = x - 5
console.log(x); // Output: 15

let y = 50;
y *= 2; // Can be written as y = y * 2
console.log(y); // Output: 100

let z = 8;
z /= 2; // Can be written as z = z / 2
console.log(z); // Output: 4

Question 8

Other mathematical assignment operators include the increment operator (++) and decrement operator (–).

The increment operator will increase the value of the variable by 1. The decrement operator will decrease the value of the variable by 1. For example:

Answer 8

let a = 10;
a++;
console.log(a); // Output: 11

let b = 20;
b–;
console.log(b); // Output: 19

Question 9

The + operator can be used to combine two string values even if those values are being stored in variables:

Answer 9

let myPet = ‘armadillo’;
console.log(‘I own a pet ‘ + myPet + ‘.’);
// Output: ‘I own a pet armadillo.’

Question 10

In the ES6 version of JavaScript, we can insert, or interpolate, variables into strings using template literals. Check out the following example where a template literal is used to log strings together:

const myPet = ‘armadillo’;
console.log(I own a pet ${myPet}.);
// Output: I own a pet armadillo.

!One of the biggest benefits to using template literals is the readability of the code.!

Answer 10

a template literal is wrapped by backticks `

Inside the template literal, you’ll see a placeholder, ${myPet}. The value of myPet is inserted into the template literal.

When we interpolate I own a pet ${myPet}., the output we print is the string: ‘I own a pet armadillo.’

Question 11

While writing code, it can be useful to keep track of the data types of the variables in your program. If you need to check the data type of a variable’s value, you can use the typeof operator.

The typeof operator checks the value to its right and returns, or passes back, a string of the data type.

Answer 11

const unknown1 = ‘foo’;
console.log(typeof unknown1); // Output: string

const unknown2 = 10;
console.log(typeof unknown2); // Output: number

const unknown3 = true;
console.log(typeof unknown3); // Output: boolean