Function expression in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a named function expression

What is the output of this code?

Javascript

const greet = function sayHello() { return 'Hello!'; };
console.log(greet());
console.log(typeof sayHello);

A ReferenceError

B

"Hello!"
"function"

C

"Hello!"
"undefined"

D

"undefined"
"undefined"

💡 Hint

Remember that the function name inside a named function expression is not accessible outside its own scope.

The function expression assigns a function named sayHello to the variable greet. Calling greet() returns 'Hello!'. However, sayHello is not defined in the outer scope, so typeof sayHello returns 'undefined'.

❓ Predict Output

intermediate

Output of an anonymous function expression assigned to a variable

What will this code print?

Javascript

const multiply = function(a, b) { return a * b; };
console.log(multiply(3, 4));

A 12

B undefined

C NaN

D TypeError

💡 Hint

The function multiplies two numbers and returns the result.

The anonymous function takes two arguments and returns their product. Calling multiply(3, 4) returns 12.

❓ Predict Output

advanced

Output of a self-invoking function expression

What is the output of this code?

Javascript

console.log((function(x) {
  return x * x;
})(5));

A undefined

B 25

C ReferenceError

D TypeError

💡 Hint

This function runs immediately with argument 5.

The function is immediately invoked with 5, returning 5 * 5 = 25.

❓ Predict Output

advanced

Output of a function expression inside an object

What will this code output?

Javascript

const obj = {
  value: 10,
  getValue: function() { return this.value; }
};
const getValue = obj.getValue;
console.log(obj.getValue());
console.log(getValue());

A

undefined
undefined

B

10
10

C

TypeError
TypeError

D

10
undefined

💡 Hint

Consider what 'this' refers to in each call.

obj.getValue() is called as a method, so 'this' refers to obj and returns 10. getValue() is called as a standalone function, so 'this' is undefined in strict mode, returning undefined.

🧠 Conceptual

expert

Why use function expressions over function declarations?

Which of the following is the main advantage of using function expressions instead of function declarations?

A Function expressions can be anonymous and assigned to variables, allowing more flexible and dynamic code.

B Function expressions are hoisted completely, so they can be called before they are defined.

C Function expressions always run faster than function declarations.

D Function expressions automatically bind 'this' to the global object.

💡 Hint

Think about how function expressions can be used in different ways compared to declarations.

Function expressions can be anonymous and assigned to variables or passed as arguments, enabling flexible and dynamic programming patterns. Function declarations are hoisted, but expressions are not. Performance and 'this' binding are not guaranteed advantages.