A Complete Guide - Web Designing JavaScript Control Structures and Functions
Web Designing: JavaScript Control Structures and Functions
JavaScript Control Structures
Control structures are a core part of JavaScript that influence the flow of execution within a script. They enable scripts to make decisions and perform iterations, making them more responsive and adaptive. Here are some essential JavaScript control structures:
If Else Statements:
if: Executes a block of code if a specified condition is true.else: Executes a block of code if the same condition is false.else if: Provides additional conditions to test if the firstifor anotherelse ifis false.
Example:
let num = 5; if (num > 10) { console.log("Number is greater than 10"); } else if (num > 5) { console.log("Number is between 5 and 10"); } else { console.log("Number is 5 or less"); }Switch Statements:
- The
switchstatement evaluates an expression and executes the corresponding block based on matching cases.
Example:
let day = "Monday"; switch (day) { case "Monday": console.log("Start of the work week."); break; case "Tuesday": console.log("It's Tuesday, just get through it."); break; default: console.log("Let's hope it's Friday!"); }- The
For Loop:
- Iterates a block of code a specified number of times.
Example:
for (let i = 0; i < 5; i++) { console.log("Iteration number: " + i); }While and Do While Loops:
Whileloop: Repeats a statement or a block of statements while a specified condition is true.Do Whileloop: Similar towhile, but the loop will always be executed at least once, even if the condition is false.
Example:
let i = 0; while (i < 5) { console.log("While Loop: " + i); i++; } i = 0; do { console.log("Do While Loop: " + i); i++; } while (i < 5);
JavaScript Functions
Functions are reusable blocks of code that perform specific tasks and can be called whenever required. They enhance the modularity, readability, and reusability of JavaScript code. Here’s an in-depth look at functions:
Function Declaration:
- Defined with the
functionkeyword, followed by a name, parentheses (which may include parameters), and a block of code to execute.
Example:
function greet(name) { console.log("Hello, " + name + "!"); } greet("Alice"); // Output: Hello, Alice!- Defined with the
Function Expressions:
- Functions can also be defined as expressions and can be stored in variables or passed as arguments.
Example:
let sayHello = function(name) { console.log("Hello, " + name + "!"); }; sayHello("Bob"); // Output: Hello, Bob!Arrow Functions:
- Introduced in ES6, arrow functions provide a shorter syntax for writing function expressions.
Example:
const multiply = (a, b) => a * b; console.log(multiply(5, 3)); // Output: 15Returning Values:
- Functions can return data to the caller using the
returnstatement.
Example:
function add(a, b) { return a + b; } console.log(add(5, 7)); // Output: 12- Functions can return data to the caller using the
Default Parameters and Rest Parameters:
- Default Parameters: Assign default values to function parameters.
- Rest Parameters: Enables a function to accept an indefinite number of arguments as an array.
Example:
Online Code run
Step-by-Step Guide: How to Implement Web Designing JavaScript Control Structures and Functions
Control Structures in JavaScript
1. If Statement
The if statement executes a statement if a specified condition is truthy.
Example:
<!DOCTYPE html>
<html>
<head>
<title>JavaScript If Statement</title>
</head>
<body>
<script>
let number = 10;
if (number > 5) {
document.write("The number is greater than 5.");
}
</script>
</body>
</html>
2. If...else Statement
The if...else statement executes a statement if the condition is truthy and another statement if the condition is falsy.
Example:
<!DOCTYPE html>
<html>
<head>
<title>JavaScript If...else Statement</title>
</head>
<body>
<script>
let number = 3;
if (number > 5) {
document.write("The number is greater than 5.");
} else {
document.write("The number is not greater than 5.");
}
</script>
</body>
</html>
3. If...else if...else Statement
The if...else if...else statement executes different statements based on multiple conditions.
Example:
<!DOCTYPE html>
<html>
<head>
<title>JavaScript If...else if...else Statement</title>
</head>
<body>
<script>
let number = 5;
if (number < 0) {
document.write("The number is negative.");
} else if (number === 0) {
document.write("The number is zero.");
} else {
document.write("The number is positive.");
}
</script>
</body>
</html>
4. Switch Statement
The switch statement evaluates an expression and executes statements in the case block that matches the expression’s value.
Example:
<!DOCTYPE html>
<html>
<head>
<title>JavaScript Switch Statement</title>
</head>
<body>
<script>
let day = 2;
let dayName;
switch (day) {
case 1:
dayName = "Monday";
break;
case 2:
dayName = "Tuesday";
break;
case 3:
dayName = "Wednesday";
break;
default:
dayName = "Another day";
}
document.write("Today is " + dayName);
</script>
</body>
</html>
Functions in JavaScript
1. Basic Function
Functions are blocks of code designed to perform a particular task.
Example:
<!DOCTYPE html>
<html>
<head>
<title>JavaScript Basic Function</title>
</head>
<body>
<script>
function greet() {
document.write("Hello, welcome to our website!");
}
greet(); // Calling the function
</script>
</body>
</html>
2. Function with Parameters
Functions can take input values, known as parameters, which can be used in the function's body.
Example:
<!DOCTYPE html>
<html>
<head>
<title>JavaScript Function with Parameters</title>
</head>
<body>
<script>
function greetUser(username) {
document.write("Hello, " + username + "! Welcome to our website!");
}
greetUser("Alice"); // Calling the function with a parameter
</script>
</body>
</html>
3. Function with Return Statement
Functions can return a value to the caller.
Example:
<!DOCTYPE html>
<html>
<head>
<title>JavaScript Function with Return Statement</title>
</head>
<body>
<script>
function add(a, b) {
return a + b;
}
let result = add(5, 3); // Calling the function and storing its result in a variable
document.write("The sum is: " + result);
</script>
</body>
</html>
Combining Control Structures and Functions
You can combine control structures and functions to create more complex and dynamic web applications.
Example:
<!DOCTYPE html>
<html>
<head>
<title>Combining Control Structures and Functions</title>
</head>
<body>
<script>
// Function to determine the grade based on score
function determineGrade(score) {
if (score >= 90) {
return "A";
} else if (score >= 80) {
return "B";
} else if (score >= 70) {
return "C";
} else if (score >= 60) {
return "D";
} else {
return "F";
}
}
let studentScore = 85;
let grade = determineGrade(studentScore);
document.write("The student's grade is: " + grade);
</script>
</body>
</html>
This example defines a function determineGrade that takes a score as a parameter and returns the corresponding grade. A student's score is passed to this function, and the resulting grade is displayed on the webpage.
Top 10 Interview Questions & Answers on Web Designing JavaScript Control Structures and Functions
1. What are Control Structures in JavaScript?
Answer: Control structures in JavaScript are constructs used to control the flow of execution in programs by making decisions and performing iterative loops. JavaScript supports several types of control structures, including if statements, switch statements, for loops, while loops, and do...while loops.
2. How do you use if statements in JavaScript?
Answer: The if statement is used to execute a block of code only if a specified condition is true. Optionally, you can include else or else if clauses to specify alternate blocks of code that should run under different conditions.
let num = 10;
if (num > 0) {
console.log("Number is positive");
} else if (num < 0) {
console.log("Number is negative");
} else {
console.log("Number is zero");
}
3. Can you explain the switch statement in JavaScript?
Answer: The switch statement is used to execute one block of code among many. It evaluates an expression and executes the case corresponding to the matching value. It's useful for replacing a series of if-else statements when you are comparing the same variable to multiple values.
let fruit = "apple";
switch (fruit) {
case "banana":
console.log("It's a banana");
break;
case "apple":
console.log("It's an apple");
break;
default:
console.log("Unknown fruit");
}
4. What are Loops in JavaScript?
Answer: Loops in JavaScript are used to execute a block of code repeatedly until a specified condition is met. JavaScript supports three types of loops: for, while, and do...while.
forloop: Executes a block of code a number of times.whileloop: Executes a block of code as long as a specified condition is true.do...whileloop: Executes a block of code at least once, then continues to execute it as long as a condition is true.
5. How can you create a function in JavaScript?
Answer: Functions in JavaScript are blocks of code designed to perform a particular task. You can create a function using the function keyword, followed by a name, parentheses, and curly braces containing the function's code.
function greet(name) {
return "Hello, " + name + "!";
}
console.log(greet("Alice")); // Output: Hello, Alice!
6. What is a callback function in JavaScript?
Answer: A callback function is a function passed into another function as an argument, which is then invoked inside the outer function to complete some kind of routine or action. Callbacks are often used in asynchronous programming.
function fetchData(callback) {
setTimeout(() => {
callback("Data fetched");
}, 1000);
}
fetchData((data) => {
console.log(data); // Output: Data fetched
});
7. Explain the difference between var, let, and const in JavaScript.
Answer: var, let, and const are all used to declare variables in JavaScript, but they have different rules and behavior:
var: Function-scoped or globally-scoped. Hoisted to the top of its scope. Can be redeclared and updated.let: Block-scoped. Hoisted to the top of its scope but not initialized (results inReferenceError). Can be updated but not redeclared within the same scope.const: Block-scoped. Hoisted but not initialized. Can neither be updated nor redeclared.
var a = 1;
let b = 2;
const c = 3;
8. What is an arrow function in JavaScript?
Answer: Arrow functions provide a more concise syntax for writing function expressions. They do not have their own bindings to this, arguments, super, or new.target.
const add = (x, y) => x + y;
console.log(add(2, 3)); // Output: 5
9. How do you handle errors in JavaScript?
Answer: JavaScript provides the try...catch statement for handling runtime errors. The try block contains code that might throw an error, and the catch block handles the error. Optionally, you can use a finally block to run code that should always execute, regardless of whether an error occurs.
try {
throw "An error occurred!";
} catch (error) {
console.error(error); // Output: An error occurred!
} finally {
console.log("This always runs.");
}
10. What is the purpose of the return statement in a function?
Answer: The return statement is used to exit a function and optionally pass a value back to the code that called the function. When a return statement is executed, the function stops executing and returns the specified value. If no value is provided, the function returns undefined by default.
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