Beginner's TypeScript #1

⭐ The Implicit ‘Any’ Type Error ⭐

We have this addTwoNumbers function:

export const addTwoNumbers = (a, b) => {
  return a + b
}

This function takes in a and b and adds them together.

It looks like perfectly valid JavaScript. But TypeScript is not happy.

We get the following errors along with the line of code where they happen:

Parameter 'a' implicitly has an 'any' type.
Parameter 'b' implicitly has an 'any' type.

This error occurs because TypeScript does not have enough information to infer a type, so it defaults to any.

👉 Solution:

The solution is to add type annotations to the function’s arguments.

In this case, both a and b should be typed as number:

export const addTwoNumbers = (a: number, b: number) => {
  return a + b
}

✍️ Summary:

TypeScript relies on type annotations to understand the contracts the function must meet. Type annotations are critical to understanding TypeScript.

Whenever we create a function, we must always specify the types of each argument!

To avoid this missing, I recommend turning on strict mode for all TypeScript projects.

When strict mode is enabled, we will get the implicitly has ‘any’ type error whenever you leave type annotations out.

I hope you found it useful. Thanks for reading. 🙏

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