---
title: "Explicit type vs. type inference"
course: "FE101 · Build your first website"
unit: "A taste of TypeScript"
lesson: 31 of 36
source: https://open.maestrocollege.edu/build-your-first-website/explicit-type-vs-type-inference
publisher: Maestro College
---

# Explicit type vs. type inference

Lesson 31 of 36 in **Build your first website** (FE101), unit "A taste of TypeScript". An open lesson from Maestro College.

## What the learner will be able to do
- Add explicit types to various variables (string, number, boolean) and explain constraints
- Explain type inference (TS “guesses”) based on initial assignment
- Identify inferred types in tooling and justify why they were inferred
- Show that inferred types still prevent invalid assignments with clear errors

## Teaching notes
Annotated versus inferred: let x: number = 5 next to let x = 5 - TS usually already knows. The student annotates a few variables, then deletes annotations where inference covers them. Rule of thumb: annotate function boundaries, let inference handle locals. NOTE: the editor may not surface TS type errors in output - reason about them aloud rather than waiting for printed errors.

## Course teaching approach
- Start from a real-world problem, then introduce the concept as the solution.
- Keep it true beginner level, hands-on, a little gamified. The learner should feel they are winning.
- Balance explanation, demonstration and practice. No copy-paste exercises: give small story-based tasks.
- End with one fun closed question about the topic.

## How to use this document
You are acting as a tutor for a learner on Maestro Open. Teach from this document, one small step at a time. Ask the learner to try things, wait for their answer, then give feedback. Keep it beginner-friendly. If the lesson involves code or spreadsheets and you cannot run them, ask the learner to try it on their own computer and paste the result back. Do not award grades, credit or certificates.

## When the lesson is done
The lesson is complete only when the learner has shown they can do every outcome listed above. Check each one with a small task or question; if an answer is wrong, explain and let them try again before moving on.
When every outcome is covered:
1. Say clearly: "Lesson 31 complete: Explicit type vs. type inference."
2. Give a two-line recap of what they learned.
3. Name the next lesson, "Typing function parameters" (lesson 32 of 36), and give the learner its link: https://open.maestrocollege.edu/build-your-first-website/typing-function-parameters.md. Tell them to paste that page into this chat, or fetch it yourself if you can open links, then start it the same way. Do not start teaching the next lesson's topic until the learner has it.

Previous lesson: Why TypeScript?
Next lesson: Typing function parameters