A tuple is a typed array with a pre-defined length and types for each index.
Tuples are great because they allow each element in the array to be a known type of value.
To define a tuple, specify the type of each element in the array:
Example:
// define our tuple
let ourTuple: [number, boolean, string];
// initialize correctly
ourTuple = [5, false, "Coding God was here"];
As you can see we have a number, boolean and a string. But what happens if we try to set them in the wrong order:
Example:
// define our tuple
let ourTuple: [number, boolean, string];
// initialized incorrectly which throws an error
ourTuple = [false, "Coding God was mistaken", 5];
Even though we have a boolean, string, and number the order matters in our tuple and will throw an error.
A good practice is to make your tuple readonly.
Tuples only have strongly defined types for the initial values:
Example:
// define our tuple
let ourTuple: [number, boolean, string];
// initialize correctly
ourTuple = [5, false, "Coding God was here"];
// We have no type safety in our tuple for indexes 3+
ourTuple.push("Something new and wrong");
console.log(ourTuple);
You see the new valueTuples only have strongly defined types for the initial values:
Example:
// define our readonly tuple
const ourReadonlyTuple: readonly [number, boolean, string] = [
5,
true,
"The Real Coding God",
];
// throws error as it is readonly.
ourReadonlyTuple.push("Coding God took a day off");
To learn more about access modifiers like readonly go to our section on them here: TypeScript Classes.
If you have ever used React before you have worked with tuples more than likely.
useState returns a tuple of the value and a setter function.
const [firstName, setFirstName] = useState('Noyon') is a common example.
Because of the structure we know our first value in our list will be a certain value type in this case a string and the second value a function.
Named tuples allow us to provide context for our values at each index.
Example:
const graph: [x: number, y: number] = [55.2, 41.3];
Named tuples provide more context for what our index values represent.
Since tuples are arrays we can also destructure them.
Example:
const graph: [number, number] = [55.2, 41.3];
const [x, y] = graph;
To review destructuring check it out here.