Learn React with TypeScript 3

Optional tuple elements

The final tuple enhancement in TypeScript 3 is the ability to have optional elements. Optional elements are specified using a ? at the end of the element type.

Let's look at another example using our scores theme:

1. Let's create a type for between one and three scores:

   type Scores = [number, number?, number?];

2. So, we should be able to create variables to hold between one and three scores:

const samScores: Scores = [55];const bobScores: Scores = [95, 75];const jayneScores: Scores = [65, 50, 70];

As expected, this compiles just fine.

3. What about four elements? Let's give this a go:

 const sarahScores: Scores = [95, 50, 75, 75];

We get a compilation error, as we would expect:

4. If we try no elements, we again get ...