Declare an array in TypeScript

Article published on my blog here :

https://alsohelp.com/blog/typescript-declare-array

How to declare an array in TypeScript the right way. A small recap, mostly note to self.

First, this is how you declare an array in JS :

In JS

const fruits = ['apple', 'orange', 'banana'];

Remember that TS generates JS, so you always end up with the above.

In TS

In TS, it will look like this:

const fruits: string[] = ['apple', 'orange', 'banana'];

You are telling TS "I'm declaring an array of string".

In TS, you always declare an array of something.

• an Array of string,
• an Array of number,
• an Array of MyType,

and so on.

Things to avoid

There is no "array of nothing" in TS.

❌ const fruits: [] = []
// wrong! you are declaring an empty array

❌ const fruits = [1, 2, 3]
// wrong! you are declaring an "array of any", like in JS

❌ const fruits: any[] = [1, 2, 3]
// wrong! you are using any, which is almost forbidden in TS

Summary

An array in TS is always an "array of something". I think it's the only gotcha to remember.

Best,

David