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castingflowtype

How can Flow be forced to cast a value to another type?

Is it possible to forcibly cast a variable in Flow?

type StringOrNumber = string | number
const foo: StringOrNumber = 'hello'

// I look for something like `const bar:string = (string) foo`
const bar: string = foo // fails
const bar: string = (foo: string) // also fails
Solution

  • Flow doesn't do direct casting from one type to another, but you can do something like

    const bar: string = (foo: any);

    so you cast foo to an any, because any accepts any type of value as an input. Then because the any type also allows you to read all possible types from it, you can assign the any value to bar because an any is also a string.