Variables

Declare & assign

You can declare and assign value to a variable.

let username;
username = 'DabAZ';

const

Use by default for values that never change.

const taxRate = 0.1;

let

Use only when the value needs to be updated.

let age = 20;
age = 20 + 1;
console.log(age);

21

var

Don't use var. It allows variables to be redeclared, which lead to bugs.

var name = "John";

Naming conventions

Only use the following naming conventions:

• Camel case: myFirstVariable
• Pascal case: MyFirstVariable
• Snake case: my_first_variable
• Constant case: MY_FIRST_VARIABLE
• Totally lower case: myfirstvariable

The camel case myFirstVariable is the most common and recommended naming convention.

const myFirst Variable = 'Hello, world!';
const 'myFirstVariable' = 'Hello, world!';
const 1FirstVariable = 'Hello, world!';

Make sure you're clearly specifying what does the variable represent.

Types

typeof

Use the typeof operator to get the type of a variable.

const age = 20;
console.log(typeof age);

number

TypeScript

TypeScript is a superset of JavaScript that adds static typing.

const age: number = 20;

Implicit conversion

In this case, the age variable is converted to a string and concatenated with the name variable.

const age = 20;
const name = 'John';
console.log(age + name);

20John

Explicit conversion

In this case, we specify the type that the number1 variable should be converted to.

const number1 = '20';
const number2 = 30;
console.log(Number(number1) + number2);

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