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var message = "Hello, World!";
var count = 10;
2. let: Introduced in ES6, let allows you to declare block-scoped variables. Block scope refers to variables that are only accessible within the block of code where they are declared, such as within a function, loop, or conditional statement.
Example:
let message = "Hello, World!";
let count = 10;
3. const: Also introduced in ES6, const is used to declare block-scoped variables that are read-only, meaning their value cannot be reassigned once initialized. const variables must be assigned a value at the time of declaration.
Example:
const pi = 3.14;
const maxCount = 100;
It’s important to note that variables declared with var are hoisted, which means they are moved to the top of their scope during the compilation phase, regardless of where they are declared within the block. However, their assignment remains in place, so variables declared with var are initialized with the value undefined until their assignment statement is reached.
Variables declared with let and const are not hoisted and follow a temporal dead zone (TDZ) before their declaration. This means you cannot access them before they are declared in the code.
Additionally, JavaScript allows you to declare multiple variables in a single statement using comma separation:
let firstName = "John", lastName = "Doe", age = 30;
By declaring variables in JavaScript, you can assign values, update them as needed, and use them to store and manipulate data throughout your code.
var message = "Hello, World!";
var count = 10;
2. let: Introduced in ES6, let allows you to declare block-scoped variables. Block scope refers to variables that are only accessible within the block of code where they are declared, such as within a function, loop, or conditional statement.
Example:
let message = "Hello, World!";
let count = 10;
3. const: Also introduced in ES6, const is used to declare block-scoped variables that are read-only, meaning their value cannot be reassigned once initialized. const variables must be assigned a value at the time of declaration.
Example:
const pi = 3.14;
const maxCount = 100;
It’s important to note that variables declared with var are function-scoped and can be hoisted, which means they are moved to the top of their scope during the compilation phase. Hoisting allows you to access variables before their declaration. However, their assignment remains in place, so variables declared with var are initialized with the value undefined until their assignment statement is reached.
Variables declared with let and const are block-scoped and are not hoisted. They follow a temporal dead zone (TDZ) before their declaration, which means you cannot access them before they are declared in the code.
Additionally, JavaScript allows you to declare multiple variables in a single statement using comma separation:
let firstName = "John", lastName = "Doe", age = 30;
By declaring variables in JavaScript, you can assign values, update them as needed, and use them to store and manipulate data throughout your code.
const constantName = initialValue;
Here’s an example of declaring and using a constant in JavaScript:
const pi = 3.14159;
const message = "Hello, World!";
const isActive = true;
console.log(pi); // Output: 3.14159
console.log(message); // Output: Hello, World!
console.log(isActive); // Output: true
In the above example, pi, message, and isActive are constants. Once assigned, their values cannot be changed throughout the execution of the program. If you attempt to reassign a value to a constant, it will result in a syntax error:
const pi = 3.14159;
pi = 3.14; // Error: Assignment to constant variable
It’s important to note that constants in JavaScript are block-scoped, meaning they are accessible only within the block of code in which they are declared. This behavior is similar to variables declared with let.
Constants are commonly used when you want to define values that should remain constant throughout the execution of your program, such as mathematical constants, configuration values, or any other value that should not be modified. Using constants can help prevent accidental reassignment and make your code more maintainable.
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