Function type declaration for flowtype

flow_func.js

//@flow

// define the function type

type FunctionThatTakesAStringAndReturnsANumber = (x: string) => number;


function higherOrderFunction(myFn: FunctionThatTakesAStringAndReturnsANumber) {
     return "something";
}

// or define the type inline

function higherOrderFunction2(myFn: (x: string) => number) {
     return "something";
}


higherOrderFunction(function (x: string) {
    return 3;
});


higherOrderFunction(function (x) {
    return "ustun"
})


higherOrderFunction2(function (x) {
    return "ozgur"
})