Why is addition in TypeScript weird? [closed]

Question

I don't know why the addition using parameter in TypeScript is weird.

const getDir = (lastIndex: number) => {
// my other code
console.log(lastIndex + 10) // result is 1010
}

getDir(10);

The result is showing 1010 instead 20.

Anyone have an idea what I do wrong?

Answer 1

Specifying a type in TypeScript does not handle the conversion. You have to do that yourself.

In your example, the argument being passed to your getDir function is a string and not a number.

The exact code you have posted in your answer does what you want it to (produces 20). You can check that out here

If you don't handle the conversion, string + string in javascript will be a concatenation and not an addition.

There are multiple ways to convert strings to number in JavaScript. The most simple way is to throw a + in front of your number. (+'10' + 10)

Example:

console.log('Should be 20: ', 10 + 10)
console.log('Should be 1010: ', '10' + 10)
console.log('Should be 20: ', +'10' + 10)