Study JavaScript #4 – Data Types

JavaScript is a loosely typed language, meaning variables do not require explicit type declarations like in languages such as Java or C. Instead, the data type of a variable is determined dynamically based on the assigned value. JavaScript data types can be broadly categorized into two types:

1. Primitive Types
2. Reference Types

Let’s explore these categories in detail.

1. Primitive Data Types

Primitive types are immutable and hold a single value. JavaScript includes the following primitive types:

1.1 Number

• JavaScript does not differentiate between integers and floating-point numbers; all numerical values are of type Number.
• Conversion functions such as parseInt() and parseFloat() allow for type conversion from strings to numbers.

var intNum = 10;
var floatNum = 0.1;
var result = 7 / 2;

console.log(result); // 3.5
console.log(Math.floor(result)); // 3
console.log(typeof result); // "number"

1.2 String

• Strings can be enclosed in single ('), double ("), or backticks (`) for template literals.
• JavaScript does not have a separate char type like Java or C.

var str = 'hello';
console.log(str[0]); // h
console.log("hello".length); // 5

var name = "John", drink = "coffee";
var message = `My name is ${name}, and I like ${drink}.`;
console.log(message); // "My name is John, and I like coffee."

1.3 Boolean

• Boolean values are either true or false.

var isTrue = true;
var comparison = (2 > 1); // true
console.log(typeof isTrue); // "boolean"

1.4 Undefined

A variable that has been declared but not assigned a value is undefined.

var notAssigned;
console.log(typeof notAssigned); // "undefined"

1.5 Null

null represents the intentional absence of a value and is considered an object.

var emptyValue = null;
console.log(typeof emptyValue); // "object"

2. Reference Types

Reference types store multiple values and are mutable. Unlike primitive types, reference types are stored as memory references.

2.1 Objects

Objects are collections of key-value pairs.

Creating Objects

Using Object Constructor:

var person = new Object();
person.name = "Alice";
person.age = 25;

Using Object Literal:

var person = {
    name: "Alice",
    age: 25
};

Using Constructor Function:

function Person(name, age) {
    this.name = name;
    this.age = age;
}
var person1 = new Person("Alice", 25);

Accessing Object Properties

Dot Notation:

console.log(person.name); // Alice

Bracket Notation:

console.log(person["age"]); // 25

Deleting Object Properties

delete person.age;

Iterating Over Object Properties

for (var key in person) {
    console.log(`Property: ${key}, Value: ${person[key]}`);
}

2.2 Arrays

Arrays store multiple values and are zero-indexed.

Creating Arrays

Using Array Literal:

var fruits = ["Apple", "Banana", "Cherry"];

Using Array Constructor:

var numbers = new Array(1, 2, 3);
console.log(numbers); // [1, 2, 3]

2.3 Functions

Functions are objects that execute specific tasks and can be assigned to variables.

var add = new Function("a", "b", "return a + b;");
console.log(add(3, 4)); // 7

Conclusion

JavaScript provides a variety of data types, each serving different purposes. Understanding the difference between primitive and reference types is fundamental to writing efficient code. In the next post, we will explore JavaScript operators and functions in more depth.