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In JavaScript, a statement is a complete unit of code that performs an action or task. A statement can be as simple as declaring a variable or as complex as a loop or a conditional statement. Each statement performs a specific action and helps to control the flow of the program.
There are several types of statements in JavaScript. Let's explain each of them with detailed examples:
1. Variable Declaration Statement:
A variable declaration statement is used to declare a variable and optionally initialize it with a value.
Example:
let message = "Hello, world!"
In this example, we declare a variable named message and initialize it with the string "Hello, world!".
2. Expression Statement:
An expression statement consists of an expression that is evaluated and produces a value.
Example:
let x = 10;
let y = 5;
let result = x + y
In this example, we use the + operator to add the values of x and y and store the result in the result variable.
3. Assignment Statement:
An assignment statement is used to assign a value to a variable.
Example:
let age = 25;
age = age + 1
In this example, we first assign the value 25 to the age variable. Then, we increment the value of age by 1 using the + operator and reassign it to the age variable.
4. Conditional Statement (if...else):
A conditional statement allows the program to make decisions based on certain conditions. It uses the if, else if, and else keywords.
Example:
let hour = 14;
let greeting;
if (hour < 12) {
greeting = "Good morning!";
} else if (hour < 18) {
greeting = "Good afternoon!";
} else {
greeting = "Good evening!";
In this example, the program checks the value of the hour variable and sets the greeting variable based on the time of the day.
5. Loop Statement (for): A loop statement allows you to repeat a block of code multiple times. The for loop is commonly used for this purpose.
Example:
for (let i = 0; i < 5; i++) {
console.log("Iteration " + (i + 1));
}
In this example, the for loop executes the code block five times, printing "Iteration 1" to "Iteration 5" to the console.
6. Function Declaration Statement:
A function declaration statement is used to define a reusable block of code that can be called later in the program.
Example:
function greet(name) {
return "Hello, " + name + "!";
}
let message = greet("Alice");
console.log(message); // Output: Hello, Alice!
In this example, we define a function named greet that takes a name parameter and returns a greeting message.
These are some of the fundamental types of statements in JavaScript. Understanding how to use these statements is essential for writing JavaScript code effectively and performing various tasks in your web applications.