String concatenation in output in Javascript

Introduction

String concatenation helps you join words or messages together to show in the output.

When you want to greet someone by name, like 'Hello, John!'

When you want to show a sentence made from different parts, like 'I have 3 apples.'

When you want to combine a number and text to explain a result.

When you want to build a message step-by-step before showing it.

Syntax

Javascript

let message = 'Hello, ' + name + '!';
console.log(message);

Use the + sign to join strings and variables together.

Make sure to add spaces inside quotes if you want spaces in the output.

Examples

Joins two strings directly to print 'Hello, world!'.

Javascript

console.log('Hello, ' + 'world!');

Joins a string and a variable to greet Alice.

Javascript

let name = 'Alice';
console.log('Hi, ' + name + '!');

Joins text and a number to show a message count.

Javascript

let count = 5;
console.log('You have ' + count + ' new messages.');

Sample Program

This program joins strings and variables to create a greeting and an info message, then prints both.

Javascript

let firstName = 'John';
let lastName = 'Doe';
let age = 30;

let greeting = 'Hello, ' + firstName + ' ' + lastName + '!';
let info = 'You are ' + age + ' years old.';

console.log(greeting);
console.log(info);

Important Notes

Remember to convert numbers to strings automatically by using + with strings.

You can also use template literals (backticks) for easier string joining, but + is simple and clear.

Summary

Use + to join strings and variables for output.

Add spaces inside quotes to keep words separate.

String concatenation helps build clear messages for users.

Practice

1. What does the + operator do when used between two strings in JavaScript?

easy

A. Divides the first string by the second

B. Joins the two strings together into one string

C. Multiplies the two strings

D. Subtracts the second string from the first

Solution

1. Step 1: Understand the + operator with strings

   In JavaScript, the + operator combines two strings into one continuous string.

2. Step 2: Recognize string concatenation

   When you write "Hello" + " World", it becomes "Hello World".

3. Final Answer:

   Joins the two strings together into one string -> Option B

4. Quick Check:

   String + String = Concatenation [OK]

Hint: Remember + joins strings like glue [OK]

Common Mistakes:

• Thinking + subtracts or divides strings
• Confusing + with arithmetic on strings
• Forgetting to add spaces inside quotes

2. Which of the following is the correct way to concatenate the strings "Hello" and "World" with a space between them in JavaScript?

easy

A. "Hello" - " " - "World"

B. "Hello" + "World"

C. "Hello" + " " + "World"

D. "Hello" * "World"

Solution

1. Step 1: Identify how to add space between words

   To add a space, include " " (space inside quotes) between the two strings.

2. Step 2: Use + operator to join all parts

   Use + to join "Hello", " ", and "World" to get "Hello World".

3. Final Answer:

   "Hello" + " " + "World" -> Option C

4. Quick Check:

   Use + and " " for spaces [OK]

Hint: Add spaces inside quotes when joining words [OK]

Common Mistakes:

• Forgetting the space string " "
• Using - or * instead of +
• Not putting quotes around the space

3. What will be the output of the following code?

let name = "Anna";
console.log("Hello, " + name + "!");

medium

A. Hello, + name + !

B. Hello, name!

C. Hello Anna

D. Hello, Anna!

Solution

1. Step 1: Understand variable substitution in concatenation

   The variable name holds the string "Anna" and is concatenated with other strings.

2. Step 2: Combine strings and variable value

   "Hello, " + name + "!" becomes "Hello, Anna!" when printed.

3. Final Answer:

   Hello, Anna! -> Option D

4. Quick Check:

   Variable value joins strings correctly [OK]

Hint: Variables inside + join as their values [OK]

Common Mistakes:

• Printing variable name instead of value
• Missing punctuation or spaces
• Using commas instead of + for concatenation

4. Find the error in this code snippet:

let greeting = "Hi";
let name = "Sam";
console.log(greeting + name);

What is missing if the output should be Hi Sam?

medium

A. A space string between greeting and name

B. Quotes around the variable name

C. A comma instead of + operator

D. Semicolon after console.log

Solution

1. Step 1: Check the concatenation result

   Currently, greeting + name joins "Hi" and "Sam" without space, resulting in "HiSam".

2. Step 2: Add a space string between variables

   Insert " " between greeting and name: greeting + " " + name to get "Hi Sam".

3. Final Answer:

   A space string between greeting and name -> Option A

4. Quick Check:

   Add " " to separate words [OK]

Hint: Add " " between words to separate them [OK]

Common Mistakes:

• Forgetting spaces in concatenation
• Using commas instead of +
• Thinking semicolon affects output

5. You want to create a greeting message that says Hello, John Doe! You have 5 new messages. using variables firstName, lastName, and messageCount. Which code correctly concatenates these values with spaces and punctuation?

hard

A. console.log("Hello, " + firstName + " " + lastName + "! You have " + messageCount + " new messages.");

B. console.log("Hello, " + firstName + lastName + "! You have " + messageCount + " new messages.");

C. console.log("Hello, " + firstName + " " + lastName + "! You have " + messageCount + "new messages.");

D. console.log("Hello, " + firstName + " " + lastName + "! You have " + messageCount + " new messages")

Solution

1. Step 1: Check spacing between first and last names

   console.log("Hello, " + firstName + " " + lastName + "! You have " + messageCount + " new messages."); adds a space string " " between firstName and lastName, correctly spacing the full name.

2. Step 2: Verify punctuation and spaces in message

   console.log("Hello, " + firstName + " " + lastName + "! You have " + messageCount + " new messages."); includes "! You have " and " new messages." with correct spaces and punctuation.

3. Final Answer:

   console.log("Hello, " + firstName + " " + lastName + "! You have " + messageCount + " new messages."); -> Option A

4. Quick Check:

   Use " " to separate names and punctuation correctly [OK]

Hint: Add spaces inside quotes between variables [OK]

Common Mistakes:

• Missing space between first and last name
• Missing space before 'new messages'
• Omitting punctuation at the end