解析Promise返回值

Question

I have a function that runs a query (returning a promise) and then manipulates the returned data. How do I get the calling function to have access to the manipulated data?

The call is like this:

getAgeGroupList().then(function (result) {
        // Would like to access manipulated data here.
    });

And the function is as below. The query.find() returns a Promise in Parse.

function getAgeGroupList(){
    var query = new Parse.Query("Fixtures_and_results");
    return query.find({
        success: function(results) {
             /* Manipulate results here, then return manipulated data */
             // How do I return the manipulated data? e.g return(newArray)
        },
        error: function(error) {  
        }
    });
}

Answer 1

If query.find returns a promise, then you don't want to use success and error handlers; instead, use then to manipulate the value:

function getAgeGroupList(){
    var query = new Parse.Query("Fixtures_and_results");
    return query.find().then(results => {
        // Manipulate results here
        return updatedResults;
    });
}

That will return a new promise that will resolve with your manipulated results rather than the original. This is promise chaining .

If the query.find call fails, its promise will reject, and the promise created by then will pass that rejection along (without calling the then handler).

---

I used an arrow function above, but looking at your code, it doesn't use any ES2015+ features other than promises. So you may want:

function getAgeGroupList(){
    var query = new Parse.Query("Fixtures_and_results");
    return query.find().then(function(results) { // <=== Changed to traditional function
        // Manipulate results here
        return updatedResults;
    });
}

instead.