TypeScript type alias for an empty array is represented by using square brackets

I have spent a lot of time delving into the typescript documentation, but I have not come across any examples that explain the use case of an empty array after the closing object brace like in the example below. I am trying to comprehend the significance of this syntax.

Any insights would be greatly appreciated!

type PostsProps = {
  posts: {
    tags?: {
      name: string
      slug: string
    }[] // curious about the purpose of this empty array
  }[] // intrigued by the purpose of this empty array
}

Answer №1

To specify an array type in TypeScript, you can use an empty array.

In the sample code snippet provided above, the empty array signifies that the posts variable is of type array containing objects with a nested property called tags, which is also an array of objects with name and slug properties, both being strings.

For instance, if I wanted to define an array type for strings, it could be done like this:

let names: string[];

names = ['John', 'Jane', 'Alice']; // This is valid

names = ['Bob', 'Sam', 123]; // This will cause an error

Answer №2

[] is a convenient shorthand for the Array type. Thus, expressions like string[] and Array<string> mean the same thing.

It's considered good practice to opt for the concise version when dealing with basic array types such as number[], string[], or any[], reserving the Array notation for more intricate types like

Array<Record<string, string>>
. Yet, TypeScript typically displays the abbreviated form (e.g., Record<string, string>[]) when describing the type upon hovering over it.

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