JavaScript Primitives

A JavaScript variable can hold 8 types of data.

7 Primitive types or an Object type.

Examples

// Number

let length = 16;

let weight = 7.5;

// BigInt

let x = 1234567890123456789012345n;

let y = BigInt(1234567890123456789012345)

// Strings

let color = "Yellow";

let lastName = "Johnson";

// Boolean

let x = true;

let y = false;

// Undefined

let x;

let y;

// Null

let x = null;

let y = null;

// Symbol

const x = Symbol();

const y = Symbol();

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JavaScript Strings

A string (or a text string) is a series of characters like "John Doe".

Strings are written with quotes. You can use single or double quotes:

Example

// Using double quotes:

let carName1 = "Volvo XC60";

// Using single quotes:

let carName2 = 'Volvo XC60';

You can use quotes inside a string, as long as they don't match the quotes surrounding the string:

Example

// Single quote inside double quotes:

let answer1 = "It's alright";

// Single quotes inside double quotes:

let answer2 = "He is called 'Johnny'";

// Double quotes inside single quotes:

let answer3 = 'He is called "Johnny"';

JavaScript Numbers

All JavaScript numbers are stored as decimal numbers (floating point).

Numbers can be written with, or without decimals:

Example

// With decimals:

let x1 = 34.00;

// Without decimals:

let x2 = 34;

Exponential Notation

Extra large or extra small numbers can be written with scientific (exponential) notation:

Example

let y = 123e5;    // 12300000

let z = 123e-5;   // 0.00123

Number Types

Most programming languages have many number types:

Whole numbers (integers): byte (8-bit), short (16-bit), int (32-bit), long (64-bit)

Real numbers (floating-point): float (32-bit), double (64-bit).

Javascript numbers are always double (64-bit floating point).

JavaScript BigInt

All JavaScript numbers are stored in a 64-bit floating-point format.

JavaScript BigInt is a new datatype (ES2020) that can be used to store integer values that are too big to be represented by a normal JavaScript Number.

Example

let x = BigInt("123456789012345678901234567890");

JavaScript Booleans

Booleans can only have two values: true or false.

Example

let x = 5;

let y = 5;

let z = 6;
(x == y)
  // Returns true
(x == z)       // Returns
  false

Booleans are often used in conditional testing.

The typeof Operator

You can use the JavaScript typeof operator to find the type of a JavaScript variable.

The typeof operator returns the type of a variable or an expression:

Example

typeof ""             // Returns
 "string"

typeof "John"         // Returns
 "string"

typeof "John Doe"     // Returns
 "string"

Example

typeof 0              // Returns
 "number"

  typeof 314            // Returns
 "number"

  typeof 3.14           // Returns
 "number"

  typeof (3)            // Returns
 "number"
typeof (3 + 4)        // Returns
 "number"

Undefined

In JavaScript, a variable without a value, has the value undefined. The type is also undefined.

Example

let car;    // Value is undefined,
    type is undefined

Any variable can be emptied, by setting the value to undefined. The type will also be undefined.

Example

car = undefined;    // Value is undefined,
    type is undefined

Empty Values

An empty value has nothing to do with undefined.

An empty string has both a legal value and a type.

Example

let car = "";    //
    The value is
    "", the typeof is "string"

Datatype null

In JavaScript, a variable or an expression can obtain the datatype null in several ways. A function can return null or a variable can be assigned the null value:

Example

let carName = null;

The strict equality operator (===) compares both the value and the type of the operands.

It returns true only if both the operands values and types are null.

The loose equality operator (==) also returns true for a null value, but it also returns true if the value is undefined.

Using == is not recommended when checking for null.