Tuple function parameters

Tuple function parameters in TypeScript 3 allow us to create strongly-typed rest parameters.

Time for an example:

1. When we first looked at rest parameters, we created a pure JavaScript version of logScores that collected an unlimited amount of arguments in a scores variable:

function logScores(...scores) {
  console.log(scores);
}

1. In TypeScript 3, we can now make this example strongly-typed with a tuple rest parameter. Let's give this a try in the TypeScript playground:

function logScores(...scores: [...number[]]) {
  console.log(scores);
}

1. Let's call our function with some scores:

logScores(50, 85, 75);

We don't get a compiler error, and if we run the program, we get an array containing 50, 85, 75 output in the console.

We can create an enhanced version of our function that uses the Scores type from the Open-ended tuples section.

1. The function will take in the name, as well as an unlimited set of scores:

type Scores = [string, ...number[]];

function logNameAndScores(...scores: Scores) {
  console.log(scores);
}

1. Let's try to call our function with some scores from Sally:

logNameAndScores("Sally", 60, 70, 75, 70);

If we run the program, Sally and her array of scores will be output to the console.