String concatenation in output in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of concatenated strings with numbers

What is the output of this JavaScript code?

console.log('5' + 3 + 2);

Javascript

console.log('5' + 3 + 2);

A '7'

B '55'

C '10'

D '532'

💡 Hint

Remember that + with a string converts numbers to strings and concatenates.

The + operator with a string converts numbers to strings and concatenates from left to right. '5' + 3 is '53', then '53' + 2 is '532'.

❓ Predict Output

intermediate

Concatenation with template literals

What will this code output?

const a = 4;
const b = 5;
console.log(`${a} + ${b} = ${a + b}`);

Javascript

const a = 4;
const b = 5;
console.log(`${a} + ${b} = ${a + b}`);

A a + b = 9

B 4 + 5 = 45

C 4 + 5 = 9

D 4 + 5 = a + b

💡 Hint

Template literals evaluate expressions inside ${}.

The template literal replaces ${a} with 4, ${b} with 5, and ${a + b} with 9, so the output is '4 + 5 = 9'.

❓ Predict Output

advanced

Output of mixed concatenation and addition

What is the output of this code?

console.log('3' + 2 * 2);

Javascript

console.log('3' + 2 * 2);

A '7'

B '34'

C '32'

D 7

💡 Hint

Remember operator precedence: * before +.

2 * 2 is 4, then '3' + 4 converts 4 to string and concatenates, resulting in '34'.

❓ Predict Output

advanced

Concatenation with null and undefined

What will this code print?

console.log('Value: ' + null + undefined);

Javascript

console.log('Value: ' + null + undefined);

A 'Value: nullundefined'

B 'Value: nullundefinedundefined'

C 'Value: nullundefinednull'

D TypeError

💡 Hint

null and undefined convert to strings when concatenated.

null converts to 'null', undefined converts to 'undefined', so concatenation results in 'Value: nullundefined'.

🧠 Conceptual

expert

Why does this concatenation produce unexpected output?

Consider this code:

console.log(1 + 2 + '3' + 4 + 5);

Why does it output '3345' instead of '12345' or a number?

A Because + is left to right, 1+2=3, then '3' + '3' = '33', then '33' + 4 + 5 = '3345'

B Because JavaScript converts all numbers to strings before adding

C Because the + operator always performs string concatenation

D Because the expression is evaluated right to left

💡 Hint

Think about how + works left to right and when it switches from addition to concatenation.

The + operator is left to right: 1+2=3 (number), then 3 + '3' converts 3 to string and concatenates to '33', then '33' + 4 = '334', then '334' + 5 = '3345'.