关于TypeScript Promise返回类型的困惑

Question

I have the following code in TypeScript React:

const AirQuality= async ():Promise<string>=>{
    console.log('Air Quality')
    let data = await fetch(url,{
        method:'GET',
        // mode:'no-cors'
    })
    return data.json()
}

As you can see here, data.json() was returned from the function. The thing I don't get is why I am not getting an error when I define the Promise type as string. What is the issue here? I changed Promise type to number, still, no error is shown. What could be the cause for that?

Answer 1

json() parses the returned JSON into a JavaScript object structure. Since this can be any kind of object depending on what the server returns, it has the type Promise<any> .

An any type can be converted to anything including number or string, which is why you don't see an error.