JavaScript Statements

JavaScript statements are programming instructions that a computer executes. A computer program is essentially a list of these "instructions" designed to perform tasks. In a programming language, such instructions are called statements.

Types of Statements

1. Variable Declarations (var, let, const)

In JavaScript, you can declare variables using var, let, or const. let and const are used in modern JavaScript for block-scoped variables, while var is function-scoped and generally considered outdated.

let name = "Mohan";   // Declaration with 'let'
const age = 25;      // Declaration with 'const' (constant value)
var isActive = true; // Declaration with 'var' (older version)

2. Assignment Statement

An assignment statement is used to assign a value to a variable. You can assign any type of value, including strings, numbers, and objects, using the assignment operator =.

let number = 10; // Assigning a number
let message = "Hello, World!"; // Assigning a string

3. Expression Statements

An expression in JavaScript is any valid unit of code that resolves to a value. When an expression is executed, it can perform an action (e.g., calculation, function call) and return a result. An expression can also be used as a statement.

x = y + 10;  // Expression statement
console.log(x); // Expression statement using a function call

4. Control Flow Statements

Control flow statements are used to control the order in which statements are executed in a program. Examples include if, else, switch, while, and for loops.

let number = 10;
if (number > 5) {
    console.log("Number is greater than 5");
}

5. Function Declarations

A function declaration is a statement that defines a function in JavaScript. Functions are reusable blocks of code designed to perform specific tasks.

function greet(name) {
    return "Hello, " + name;
}

console.log(greet("Alisha"));

6. Return Statement

The return statement is used to exit a function and optionally pass a value back to the calling code.

function add(x, y) {
    return x + y;
}
let result = add(5, 3); // result will be 8

7. Throw Statement

The throw statement is used to create custom errors in JavaScript. It is often used in conjunction with try...catch to handle errors.

function checkAge(age) {
    if (age < 18) {
        throw new Error("Age must be 18 or older");
    }
}

8. Try...Catch Statement

The try...catch statement is used to handle exceptions in JavaScript. The code inside the try block is executed, and if an error occurs, the code inside the catch block will handle the error.

try {
    let result = someUndefinedFunction(); // This will throw an error
    console.log(result);
} catch (error) {
    console.error("An error occurred:", error.message);
}

9. Break and Continue Statements

The break and continue statements are used within loops. break exits the loop, while continue skips to the next iteration.

for (let i = 0; i < 10; i++) {
    if (i === 5) {
        break;  // Exits the loop when i equals 5
    }
    console.log(i);
}

Some commonly used keywords are: