JavaScript Statements and Blocks

JavaScript Statements and Blocks – Code Structure

In JavaScript, statements are the building blocks of code that perform actions, such as assignments or function calls. Blocks are groups of statements enclosed in curly braces {}.

1. JavaScript Statements

A statement is an instruction that performs an action. For example, assignments, loops, conditionals, and function calls are all types of statements.

Types of Statements:

Expression Statement: Contains an expression that is evaluated and performs an action.
```
let x = 10; // This is an expression statement.
```
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Declaration Statement: Used to declare variables, functions, or classes.

let name; // Variable declaration statement.
function greet() {} // Function declaration statement.

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Control Flow Statements: Includes conditionals (if, else), loops (for, while), and switch.
```
if (x > 5) {
    console.log("x is greater than 5");
}
```
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Return Statement: Exits a function and optionally returns a value.
```
return 42;
```
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Break and Continue Statements: Used to control loop execution.
```
break; // Exits the loop.
continue; // Skips to the next iteration.
```
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Example of Multiple Statements:

let a = 5;  // Declaration statement
a += 10;    // Expression statement
console.log(a); // Function call statement

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2. JavaScript Blocks

A block is a group of statements enclosed in curly braces {}. Blocks are often used in control structures such as loops, conditionals, and functions to group multiple statements together.

Syntax of a Block:

{
    statement1;
    statement2;
    ...
}

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Example of a Block:

if (x > 10) {
    let result = x * 2; // This is inside the block.
    console.log(result); // This is inside the block.
}

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In the example above, the block {} groups the statements together, and the block will execute only if the condition x > 10 is true.

Blocks in Functions:

A function is a block of code that performs a task. You can have multiple statements inside the block of a function.

function calculate(a, b) {
    let sum = a + b;
    let difference = a - b;
    return sum * difference;
}

let result = calculate(10, 5); // Calls the function
console.log(result); // 75

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3. Block Scope vs Function Scope

Block Scope: Variables declared within a block (using let or const) are only accessible inside that block.
```
if (true) {
    let a = 10; // a is scoped to the block
}
console.log(a); // Error: a is not defined
```
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Function Scope: Variables declared within a function are only accessible inside that function.
```
function myFunction() {
    let x = 20;
}
console.log(x); // Error: x is not defined
```
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4. Important Notes

A semicolon ; is typically used to terminate a statement in JavaScript.
Blocks are used to group multiple statements and can be used in control structures, functions, and loops.

Conclusion:

Statements perform actions like assignments, conditionals, loops, and function calls.
Blocks group multiple statements together and are used with control structures like if, for, and while.
Understanding block scope and function scope helps you manage variable visibility in JavaScript.