Function parameters in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of function with default parameters

What is the output of the following JavaScript code?

Javascript

function greet(name = "Guest", greeting = "Hello") {
  return `${greeting}, ${name}!`;
}

console.log(greet(undefined, "Hi"));

A "Hi, Guest!"

B "Hi, undefined!"

C "Hello, Guest!"

D "Hello, undefined!"

💡 Hint

Remember that passing undefined triggers default parameters.

When you pass undefined as an argument, the default parameter is used. Here, name is undefined, so it defaults to "Guest". The greeting is "Hi" as passed.

❓ Predict Output

intermediate

Rest parameters and arguments length

What will be logged to the console when this code runs?

Javascript

function sum(...numbers) {
  return numbers.reduce((a, b) => a + b, 0);
}

console.log(sum(1, 2, 3, 4));

A undefined

B 1234

C 10

D TypeError

💡 Hint

Rest parameters collect all arguments into an array.

The rest parameter 'numbers' collects all arguments into an array [1,2,3,4]. The reduce sums them to 10.

❓ Predict Output

advanced

Parameter destructuring with default values

What is the output of this code snippet?

Javascript

function display({name = "Unknown", age = 0} = {}) {
  console.log(`${name} is ${age} years old.`);
}

display({age: 25});

A TypeError

B "Unknown is 25 years old."

C "Unknown is undefined years old."

D "undefined is 25 years old."

💡 Hint

Missing properties use default values in destructuring.

The object passed has age:25 but no name. So name defaults to "Unknown" and age is 25.

❓ Predict Output

advanced

Effect of parameter order with default and rest

What will this code output?

Javascript

function test(a, b = 2, ...rest) {
  console.log(a, b, rest.length);
}

test(1, undefined, 3, 4);

A 1 3 1

B 1 undefined 2

C 1 2 0

D 1 2 2

💡 Hint

Undefined triggers default parameter; rest collects remaining arguments.

a=1, b=undefined triggers default 2, rest collects [3,4] so length is 2.

🧠 Conceptual

expert

Understanding parameter shadowing and closures

Consider the following code. What is the value of variable 'result' after execution?

Javascript

let result;
function outer(x) {
  return function inner(x = 5) {
    result = x;
  };
}

const fn = outer(10);
fn();

A 5

B 10

C undefined

D ReferenceError

💡 Hint

Inner function parameter shadows outer parameter; default applies when no argument passed.

The inner function has a parameter x with default 5. Calling fn() passes no argument, so x=5 inside inner, assigned to result.