What's the meaning of "void = () => {}" after Fat arrow function in TypeScript?

Question

I saw this block of code in our code base and I have a bit of a problem to understand void = (page). According to https://stackoverflow.com/a/34274584/513413, the return type is coming after => which is void in my case. So what does = (page) => {} do? What is its equivalent function if I don't write it with fat arrow function?

This is the code:

private navigateTo: (page: string) => void = (page) => {
    // display page
}

Answer 1

You are looking at the code incorrectly. The general structure is

private Name: Type = Value

The type is (page: string) => void and the value is (page) => {}. The type means that navigateTo is a function that accepts a string as argument and returns nothing, which is what (page) => {} does.

Answer 2

In Typescript, typings are inserted inside the statements of the language, transforming them a bit.

The code you submitted should read as such:

• private navigateTo: This part is straighforward. We create a private member called navigateTo inside the current class.
• ...: (page: string) => void: This is the type of the member. In this case, it represents a function taking in a string parameter and not returning anything (void). This part is purely Typescript.
• ... = (page) => { /* display page */ }: This is the actual function being assigned to the variable.

I recommend you read some of the Typescript Handbook. It has a lot of information about the syntax and the language.