Array Types in TypeScript

Just like other data types, TypeScript can define the type of an array using different techniques.

Inferred Array Type

Here is a normal array variable which is initialized with an array.

const fruits = ["Apple", "Banana"];

Here is the type automatically inferred by TypeScript from the assigned array.

const fruits: string[];

Mixed Data Types

Let us have an array that has elements of different types.

const fruits = ["Apple", 23];

Now the inferred type for fruits is:

const fruits: (string | number)[];

It says that the array can contain either a string value or a number value.

Set Types Explicitly

Say, we need to declare a variable marks that will contain an array of marks which are numbers. We can declare the variable with its type like below:

let marks: number[];

Then, later we can assign a number array to marks.

marks = [23, 45];

What if we assign a string array to marks? TypeScript can throw an error.