03-Data-Types.md

Table of Content

• Data Types in JavaScript
  • Numeric Data Type
  • String Data Type
  • Boolean Data Type
  • Null Data Type
  • Undefined Data Type
  • Symbols Data Type
• Objects in JavaScript
  • Create, Read, Update and Delete (CRUD) in Objects
    • Create
    • Read
    • Update
    • Delete
    • Other Useful Methods to Know

Data Types in JavaScript

There are six types of primitive data types we use in JavaScript.

• numeric
• string
• Boolean
• null
• undefined
• symbol (introduced in ES6)

Numeric Data Type

Numeric data type handles numbers. It can be any numbers including decimal numbers like 3.14.

let number = 1;
let integer = 1.12345;
let negativeNumber = -1;
let negativeInteger = -1.1234;

String Data Type

String data type holds letters and symbols. We wrap our string of texts in quotation marks. We can use either of single('') or double quotation ("") mark. But we need to make sure we start and end with the same quotation. in some case, if we want to include the quotation in our string of texts, we can escape the string quotes by placing a backslash infornt of them.

let quote = "Everybody has a monster";
let mixedQuote = 'This keeps the "Quotation Mark".';

Boolean Data Type

Boolean data type holds the value either true or false. We can store true/false in a variable by typing them without quotation.

var isSingle = true;

Null Data Type

When we want a variable to be empty but not undefined , we set the variable to null (without quotation mark).

let salary = null;

Undefined Data Type

JavaScript is a weakly typed language, therefore the data type for variable are determined only after some value is stored in the variable. So, if no value is stored in a varibale, it is initalized as undefined.

Symbols Data Type

Symbols data types are the primitive data types introsuces in ECMAScript 2015. Once we create a symbol, its value are kept private and for internal use. All that remains is the symbol reference.

We can create a symbol by simply calling Symbol() function.

const myVariable = Symbol();

We get a new and unique symbol everytime we invoke a Symbol function(). Each symbol is guaranteed to be different from other symbols created.

Symbol() === Symbol(); //OUTPUT: false

We can also pass parameter to Symbol() function which can be useful for debugging.

console.log(Symbol("Some Test"));

We mostly use Symbols to avoid name clashing between object properties sicnce no symbol is equal to other.

const NAME = Symbol();
const person = {
  [NAME]: "Flavio",
};

person[NAME]; //'Flavio'

const RUN = Symbol();
person[RUN] = () => "Person is running";
console.log(person[RUN]());

typeof operator

If we ever want to know the data type of a certain variable, we can use typeof operator.

let name = "Prabesh";
console.log(typeof name); //OUTPUT: String

let isSingle = true;
console.log(typeof isSingle); //OUTPUT: Boolean

Objects in JavaScript

In JavaScript, EVERYTHING is an Object.

Objects are the primitibe data structure in JavaScript. We define objects using curly brackets {} and keep key-value pairs seperated by comma.

const myself = {
  firstName: "Prabesh",
  lastName: "Thapa",
  email: "[email protected]",
  nickName: "entry",
};

Create, Read, Update and Delete (CRUD) in Objects

Create

// Creating an empty object
let player = {};

player.name = "Cristiano Ronaldo";
player["sports"] = "Football"; //Using [] is also valid
player.nickname = "GOAT";
player.country = "Portugal";

console.log(player);

// OUTPUT:
// {
//     "name": "Cristiano Ronaldo",
//     "sports": "Football",
//     "nickname": "GOAT",
//     "country": "Portugal"
// }

Or, we can simply add all key-value pairs at oncce.

let player = {
  name: "Cristiano Ronaldo",
  sports: "Football",
  nickname: "GOAT",
  country: "Portugal",
};

Read

We use the . operator to access the values of an object.

player.name; //OUTPUT: "Cristiano Ronaldo
player.nickname; //OUTPUT: "GOAT"

We can also use the square brackets [] to access these properties.

player["sports"]; //OUTPUT: "Football"
player["country"]; //OUTPUT: "Portugal"

Update

We can update the value of a key by overriding the previous value.

player.name = "Cristiano Alveiro Dos Santos Ronaldo";

Delete

We can use the delete operator to remove a property from an object.

SYNTAX:

delete object.property
delete object[property]

const user = {
  firstname: "Entry",
  lastname: "Eemroy",
};

console.log(user.firstname);
// OUTPUT: "Eemroy"

delete user.firstname;

console.log(user.firstname);
// OUTPUT: undefined

Other Useful Methods to Know

Print Keys from the object

Object.keys(player);

["name", "sports", "nickname", "country"];

Print values from the object

Object.values(player);

["Cristiano Ronaldo", "Football", "GOAT", "Portugal"];

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