异步/等待根本不返回结果

Question

I don't really get the async/await method after trying to ask my lecturer and trying to surf on the web. I initially thought async/await can return me the desired outcome for my activity selection challenge, but it doesn't.

From this code given, i am trying to console.log() out the result from the function selectPerformanceByFestivalId , but then when i see the result, it only gives me an empty object as the result instead of an array of objects.

By right i was supposed to get something like this:

[
  {
    "performanceid": "1234567890",
    "starttime": 1330,
    "endtime": 1530,
    "festivalid": "2234567891"
  },
  {
    "performanceid": "1234567891",
    "starttime": 1530,
    "endtime": 1630,
    "festivalid": "2234567891"
  },
  {
    "performanceid": "1234567892",
    "starttime": 1330,
    "endtime": 1530,
    "festivalid": "2234567891"
  },
  {
    "performanceid": "1234567893",
    "starttime": 1330,
    "endtime": 1530,
    "festivalid": "2234567891"
  },
  {
    "performanceid": "1234567894",
    "starttime": 1430,
    "endtime": 1530,
    "festivalid": "2234567891"
  }
]

But i got this as the result: {} .

Here is my current async/await code:

async function sortPerformanceByFinishTime(endTime) {
    const filteredPerformance = await selectPerformanceByFestivalId;  //do a await to let the previous function execute first before continuing
    const storeArray = []   //create a new array to reorder the stuff again
    console.log(filteredPerformance);
};

This is how i did my selectPerformanceByFestivalId :

// 1. selectPerformance to correctly select set of performance for computation
function selectPerformanceByFestivalId(performances) {
    const l = performances.length;  //length of performances
    const selectedPerformance = []; //create a new array selectedPerformance
    for (let i = 0; i < l; i++) {   //iterate through all the festivalId
        selectedPerformance.push(performances[i]);  //push filtered performance into the array
    };
    return selectedPerformance; //return the array
};

selectPerformanceByFestivalId is supposed to hold the entire json result(which was the data above) and when i console.log(filteredPerformance) , i expected the same json result.

Is there anything wrong?

Answer 1

You are giving a reference to a function object instead of calling it.

Change your line of code to

  const filteredPerformance = await selectPerformanceByFestivalId(); 

Answer 2

I created a Plunk at https://plnkr.co/edit/OeJg8ISk8XHinuR3 using the example code that you have shared above. Couple of changes to your existing code.

1. Added async Keyword before the function selectPerformanceByFestivalId .
2. Added parens after the call to the function selectPerformanceByFestivalId in the function sortPerformanceByFinishTime