Dynamic typing in JavaScript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code with dynamic typing?

Consider the following JavaScript code. What will be printed to the console?

Javascript

let x = '5';
x = x + 3;
console.log(x);

A undefined

B 8

C TypeError

D "53"

💡 Hint

Remember that + operator with a string converts the other operand to string.

In JavaScript, when you add a number to a string, the number is converted to a string and concatenated. So '5' + 3 becomes '53'.

❓ Predict Output

intermediate

What is the type of variable after reassignment?

What will be the output of the following code?

Javascript

let data = 10;
data = 'hello';
console.log(typeof data);

A "number"

B "undefined"

C "string"

D "object"

💡 Hint

Variables in JavaScript can hold any type and can be reassigned.

Initially data is a number, but after reassignment it holds a string, so typeof returns 'string'.

❓ Predict Output

advanced

What is the output of this dynamic type coercion?

What will this code print to the console?

Javascript

console.log('5' - 3);

A 2

B "53"

C NaN

D TypeError

💡 Hint

The - operator converts strings to numbers if possible.

The - operator triggers numeric conversion, so '5' becomes 5 and 5 - 3 equals 2.

❓ Predict Output

advanced

What error does this code raise due to dynamic typing?

What happens when this code runs?

Javascript

let a = null;
console.log(a.toUpperCase());

A TypeError

B null

C undefined

D SyntaxError

💡 Hint

null has no methods and cannot be used like a string.

Calling a method on null causes a TypeError because null is not an object.

🧠 Conceptual

expert

Which option shows the correct dynamic type change and output?

Which code snippet will output the number 10 after dynamic typing changes?

A let val = '5'; val = val - '5'; console.log(val);

B let val = '5'; val = +val + 5; console.log(val);

C let val = 5; val = val + '5'; console.log(val);

D let val = '5'; val = val + 5; console.log(val);

💡 Hint

The unary + converts string to number before addition.

Option B converts '5' to number 5 using unary +, then adds 5 to get 10. Others produce strings or 0.