Correct way to map through tuple type parameter

When I run the function below, I get this error: "Element implicitly has an ‘any’ type because expression of type ‘0’ can’t be used to index type ‘string | number’. Property ‘0’ does not exist on type ‘string | number"
I have seen index signature examples { [key: string]: number } to solve similar issue, but I don’t think it applies to this case. What would be the correct approach to solve this issue?

function getNames(namesAndAges: [ string, number ]): string[]{
 return namesAndAges.map(val => (val[0]));
}
console.log(getNames([['Amir', 34], ['Betty', 17]]));
// expected result ['Amir', 'Betty']

>Solution :

Your argument type is wrong.

function getNames(namesAndAges: [ string, number ])

means you would need to call it with an array containing a string and a number.

getNames(['a', 5])

You want an array of arrays instead. Type it as

function getNames(namesAndAges: Array<[ string, number ]>)