JS Statements

JavaScript Statements

In JavaScript, statements are instructions that are executed by the web browser or Node.js. A statement can be a simple or complex operation that performs an action, such as assigning a value to a variable, calling a function, or controlling the program flow.

JavaScript programs are essentially a sequence of these statements. Together, they create the logical flow of the application.

There are several different types of statements in JavaScript, each serving a unique purpose.

1. Declaration Statements

Declaration statements are used to introduce variables, functions, or classes into a program. These statements begin with a keyword (like var, let, const, or function) followed by an identifier (its name).

Variables are containers for storing data values.

var x = 5;
var y = 6;
var X = 4;
var z = x + y;

console.log(z); // Outputs 11

Note: JavaScript identifiers are highly case-sensitive. Notice that the variable x is not the same as the variable X.

2. Expression Statements

Expression statements, such as function calls or assignments, evaluate an expression and generate a value in JavaScript. They can be assigned to a variable or used as part of a larger expression.

// Function call expression
console.log('Hello World');

// Assignment expression
var x = 5;
x = 6; // Re-assigning the value
console.log(x); // Outputs 6

3. Conditional Statements

Conditional statements, such as if statements or switch statements, control the flow of a program based on a specific condition evaluating to true or false.

// If statement
var x = 10;
if (x > 5) {
  console.log('x is greater than 5');
}

// Switch statement
var y = 2;
switch (y) {
  case 1:
    console.log('y is 1');
    break;
  case 2:
    console.log('y is 2'); // This will execute
    break;
  default:
    console.log('y is neither 1 nor 2');
}

4. Loop Statements

Loop statements, such as while loops or for loops, are used to repeatedly execute a block of code as long as a specified condition remains true.

Convention: The let keyword is conventionally used to declare counter variables (like i) inside for loops.

// While loop
var x = 4;
while (x < 5) {
  console.log(x); // Outputs 4
  x++;
}

// For loop
for (let i = 0; i < 5; i++) {
  console.log(i); // Outputs 0, 1, 2, 3, 4
}

5. Jump Statements

Jump statements, such as break or return statements, forcefully transfer control to another part of the program, overriding normal sequential execution.

// Break statement: Stops the loop entirely
for (let i = 0; i < 5; i++) {
  if (i === 3) {
    break; 
  }
  console.log(i); // Outputs 0, 1, 2
}

// Return statement: Exits a function and outputs a value
function add(x, y) {
  return x + y;
}
console.log(add(5, 5)); // Outputs 10