將promise數據返回給調用函數

Question

let func1 = function() {
   return new Promise((resolve,reject) => {
        let someVal = 5;
        if (condition) {
            resolve(someVal);
        }
        else {
            reject('error occured');
        }
   });
}

let callingFunction = function() {
    func1().then((res) => {
        console.log("result",res); /* want to return res to the callingFunction */
        return res; /* doesn't work as it returns to the .then not to the callingFunction I guess. */
    });
}

let finalData = callingFunction();

它是可行的，從發送結果.then承諾塊callingFunction讓我在FinalData的得到的結果？

Answer 1

let callingFunction = function() {
  return func1().then((res) => {
    console.log("result",res)
    return res
  })
}
callingFunction().then((res) => {
  let finalData = res
})

Answer 2

問題是promise是一個異步操作，因此let finalData = callingFunction(); 評估為undefined 。 如果要在callingFunction()使用promise的結果，只需將res作為參數傳遞給它，如下所示：

let func1 = function() {
   return new Promise((resolve,reject) => {
        let someVal = 5;
        if (condition) {
            resolve(someVal);
        }
        else {
            reject('error occured');
        }
   });
}

func1().then((res) => {
    console.log("result",res); /* want to return res to the callingFunction */
    callingFunction(res);
  });