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Lesson 2 — Typed functions
Typed inputs and outputs
In TypeScript you type each parameter (the inputs) and the return type (the output), which goes after the parentheses. Then every call is checked: add("2", 3) becomes an error before you run anything, and the editor knows what the function gives back.
function shout(word: string): string {
return word.toUpperCase() + "!";
}
Why it matters: functions are where values move around, so typing them catches most mix-ups at once.
Want it another way?
Task
Type a and b as numbers, make add return their sum, and print add(2, 3) → 5.
Run your code — when the output matches the task, you will see a green check. Then mark the lesson complete.
Test your knowledge
Test your knowledgeA quick 3-question quiz on this lesson — instant feedback.