Optional and default parameters

A ? after a parameter name makes it optional, and = gives it a default. Both let one function serve the common case and the detailed one without overloads.

What a session covers

The tutor works through these with you, in conversation and code. A session ends when you have shown them, not when a video does.

Explain the difference between an optional parameter and one with a default
Write a function that handles a missing argument and one that fills a default
Spot why if (!page) treats 0 as missing, and compare with undefined instead

In practice

A few lines that show Optional and default parameters doing its job.

TypeScript

function paginate(items: string[], size = 10, page?: number) {
  const start = ((page ?? 1) - 1) * size;
  return items.slice(start, start + size);
}

paginate(list);          // first 10
paginate(list, 25);      // first 25
paginate(list, 25, 3);   // third page of 25

The common mistake

Watch for

Checking an optional parameter with if (!page) when 0 or "" is a valid value. The falsy check treats them as missing; compare with undefined or use ?? instead.

What to know first

Your roadmap puts these before Optional and default parameters, unless you already know them.

Function types

How it stays learned

Once a session shows you understand Optional and default parameters, it comes back for review. Each review takes a minute and tells the memory model how well you still know it.

Day 3First recall, while it is fresh
Day 7Second, a week on
Day 18Last, when it has settled

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