Why JavaScript is widely used - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print a message in the browser console.

Javascript

console.[1]('Hello, JavaScript!');

Drag options to blanks, or click blank then click option'

Alog

Bprint

Cwrite

Dshow

Attempts:

3 left

💡 Hint

Common Mistakes

Using console.print or console.write which do not exist.

The console.log method is used to print messages to the browser console.

2fill in blank

medium

Complete the code to create a variable named 'name' with the value 'Alice'.

Javascript

let [1] = 'Alice';

Drag options to blanks, or click blank then click option'

Avar

Bname

Clet

Dconst

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'var' or 'const' as variable names instead of 'name'.

The variable name should be name as specified.

3fill in blank

hard

Fix the error in the function declaration to correctly greet a user.

Javascript

function greet([1]) {
  return `Hello, ${name}!`;
}

Drag options to blanks, or click blank then click option'

Aname

BuserName

Cuser

Dgreeting

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different parameter name than the one used inside the function.

The parameter name should be name to match the template literal inside the function.

4fill in blank

hard

Fill both blanks to create an array of numbers and get its length.

Javascript

const numbers = [[1]];
const length = numbers.[2];

Drag options to blanks, or click blank then click option'

A1, 2, 3, 4, 5

Bsize

Clength

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'size' or 'count' instead of 'length' for array size.

The array contains numbers separated by commas. The property to get the number of elements is length.

5fill in blank

hard

Fill all three blanks to create an object with a method that returns a greeting.

Javascript

const person = {
  [1]: 'Bob',
  [2]() {
    return `Hi, I am ${this.[3]`;
  }
};

Drag options to blanks, or click blank then click option'

Aname

Bgreet

DsayHello

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent names for the property and inside the method.

The object has a property name, a method greet, and inside the method it uses this.name to access the property.

Practice

1. Why is JavaScript considered essential for making websites interactive?

easy

A. Because it styles the webpage with colors and fonts

B. Because it creates static HTML pages

C. Because it stores data permanently on the server

D. Because it runs in the browser and can change webpage content dynamically

Solution

1. Step 1: Understand JavaScript's role in browsers

   JavaScript runs inside web browsers and can change webpage content without reloading.

2. Step 2: Identify how interactivity is achieved

   By changing content dynamically, JavaScript makes websites interactive, unlike static HTML or CSS.

3. Final Answer:

   Because it runs in the browser and can change webpage content dynamically -> Option D

4. Quick Check:

   JavaScript = dynamic webpage content [OK]

Hint: JavaScript changes webpage content live in browser [OK]

Common Mistakes:

• Confusing JavaScript with CSS styling
• Thinking JavaScript only runs on servers
• Believing JavaScript creates static pages

2. Which of the following is the correct way to write a JavaScript function that alerts 'Hello'?

easy

A. function sayHello[] { alert('Hello'); }

B. def sayHello() { alert('Hello'); }

C. function sayHello() { alert('Hello'); }

D. func sayHello() alert('Hello')

Solution

1. Step 1: Recall JavaScript function syntax

   JavaScript functions start with the keyword 'function', followed by name and parentheses.

2. Step 2: Check each option's syntax

   function sayHello() { alert('Hello'); } uses correct syntax with parentheses and curly braces; others use wrong keywords or brackets.

3. Final Answer:

   function sayHello() { alert('Hello'); } -> Option C

4. Quick Check:

   JavaScript function syntax = function sayHello() { alert('Hello'); } [OK]

Hint: JavaScript functions use 'function' keyword and parentheses [OK]

Common Mistakes:

• Using Python or other language keywords
• Using square brackets instead of parentheses
• Omitting curly braces

3. What will be the output of this code?

console.log(typeof window);

medium

A. 'object'

B. ReferenceError

C. 'function'

D. 'undefined'

Solution

1. Step 1: Understand the 'window' object in browsers

   'window' is a global object representing the browser window and environment.

2. Step 2: Check the typeof operator result

   typeof window returns 'object' because window is an object in JavaScript.

3. Final Answer:

   'object' -> Option A

4. Quick Check:

   typeof window = 'object' [OK]

Hint: 'window' is a browser object, so typeof is 'object' [OK]

Common Mistakes:

• Thinking 'window' is undefined outside browsers
• Confusing 'object' with 'function'
• Expecting a ReferenceError

4. Find the error in this JavaScript code snippet:

let count = 0;
if (count = 5) {
  console.log('Count is five');
}

medium

A. Missing semicolon after let declaration

B. Using assignment '=' instead of comparison '==' or '===' in if condition

C. console.log syntax is incorrect

D. Variable 'count' is not declared

Solution

1. Step 1: Analyze the if condition

   The condition uses '=' which assigns 5 to count instead of comparing values.

2. Step 2: Identify correct comparison operator

   To compare, '==' or '===' should be used, not '=' which is assignment.

3. Final Answer:

   Using assignment '=' instead of comparison '==' or '===' in if condition -> Option B

4. Quick Check:

   Use '==' or '===' for comparison, not '=' [OK]

Hint: Use '==' or '===' for comparison, not '=' [OK]

Common Mistakes:

• Confusing assignment '=' with equality check
• Ignoring missing semicolons (optional in JS)
• Assuming console.log syntax is wrong

5. JavaScript can be used on both frontend and backend. Which technology allows JavaScript to run on the server side?

hard

A. Node.js

B. React

C. Angular

D. jQuery

Solution

1. Step 1: Identify frontend and backend roles

   Frontend runs in browsers; backend runs on servers handling data and logic.

2. Step 2: Recognize server-side JavaScript technology

   Node.js is a runtime that allows JavaScript to run on servers, unlike React, Angular, or jQuery which are frontend libraries/frameworks.

3. Final Answer:

   Node.js -> Option A

4. Quick Check:

   Server-side JavaScript = Node.js [OK]

Hint: Node.js runs JavaScript on servers, others are frontend tools [OK]

Common Mistakes:

• Confusing frontend frameworks with backend runtime
• Thinking jQuery runs on servers
• Assuming React or Angular run backend code