Typescript - Wait for promise resolve before function return

Question

Updated with working solution

I start with a function that grabs information from all rows selected in a table and pushes that information into a stack for later processing.

for (var i = 0; i < this.selectedItems().length; i++) {
    var row = this.selectedItems()[i];
    let info = this.createFileReqInfo(row.Number(), FileRequestType.AssociatedDoc);
    fileReqInfo.push(info);
}

My Problem: The createFileReqInfo function returns before the asynchronous API call can return a value, so I'm not getting the right value for userCanView in the return object.

createFileReqInfo = (reportId: number, fileRequestType: FileRequestType) : any => {
    let fileReq = new FileRequest(reportId, fileRequestType);
    var uCanView = false;
    this.reportModel.getReportSecurity(reportId).done((result) => {
        uCanView = result.CanViewReport;
        var info: {
            fileRequest: FileRequest,
            userCanView: boolean
        } = {
            fileRequest: fileReq,
            userCanView: uCanView
        }
        return info;        
    });
}

The compiler won't let me use await here. Any ideas on how to get the function to block until the API call returns?

---

Solution

My problem here is that there were a few levels of function calls here that I had to rework to create and resolve promises. The function that calls the API resembles something in the suggested solutions

createFileReqInfo = (reportId: number, fileRequestType: FileRequestType) : JQueryPromise<any> => {
    let fileReq = new FileRequest(reportId, fileRequestType);
    var uCanView = false;

    var info: {
        fileRequest: FileRequest,
        userCanView: boolean
    } = {
        fileRequest: fileReq,
        userCanView: uCanView
    }

    let dfd: JQueryDeferred<any> = $.Deferred();

    this.reportModel.getReportSecurity(reportId).done((result) => {
        uCanView = result.CanViewReport;
        info.userCanView = uCanView;
        dfd.resolve(info);
    });

    return dfd;
}

This now returns a promise. The problem I had is with the function that calls this one because it iterates through a list of selected items and queues up various reports to download, but only the ones that exist in that particular selection. Had to use this answer to figure out a way to wait for all the promises to resolve before continuing.

getFileReqsFromSelectedItems = (view1: boolean, view2: boolean, view3: boolean): JQueryPromise<any> => {
    var fileReqInfo: {
        fileRequest: FileRequest,
        userCanView: boolean
    }[] = [];

    let dfd: JQueryDeferred<any> = $.Deferred();

    let promise: JQueryPromise<any>;
    let promiseArray: JQueryPromise<any>[] = [];

    for (var i = 0; i < this.selectedItems().length; i++) {
        var row = this.selectedItems()[i];

        if( view1 && row.HasView1() ) {
            promise = this.createFileReqInfo(row.Number(), FileRequestType.AssociatedDoc1);
            promiseArray.push(promise);
        }
        if( view2 && row.HasView2() ) {
            promise = this.createFileReqInfo(row.Number(), FileRequestType.AssociatedDoc2);
            promiseArray.push(promise);
        }
        if( view3 && row.HasView3() ) {
            promise = this.createFileReqInfo(row.Number(), FileRequestType.AssociatedDoc3);
            promiseArray.push(promise);
        }
    }

    $.when.apply($, promiseArray).done(function() {
        var promises = arguments;
        for (var j = 0; j < promises.length; j++)
        {
            fileReqInfo.push(promises[j]);
        }
        dfd.resolve(fileReqInfo);
    });

    return dfd;
}

After that, it was easy to take the array of returned values and pass it to the download function.

downloadReports = () => {
    this.getFileReqsFromSelectedItems(this.view1Check(), this.view2Check(), this.view3Check()).then((fileReqsDetails) => { 
        this.downloadTrialFiles(fileReqsDetails);
    });
}

Whew!

Answer 1

For APIs that don't support promises, you can use new Promise to create a promise yourself, call resolve with the result of the async call, then you can use async/await syntax when calling it. More info on promises

interface ReportSecurityInfo {
    fileRequest: FileRequest
    userCanView: boolean
}

createFileReqInfo = (reportId: number, fileRequestType: FileRequestType): Promise<any> => {
    let fileReq = new FileRequest(reportId, fileRequestType);
    var uCanView = false;

    return new Promise((resolve, reject) => {
        this.reportModel.getReportSecurity(reportId).done((result) => {
            uCanView = result.CanViewReport;
            var info: ReportSecurityInfo = {
                fileRequest: fileReq,
                userCanView: uCanView
            }
            resolve(info)
        });
    })
}

// somewhere else...
const info = await this.createFileReqInfo()

I also went ahead and split out the type of info as its own interface for readability.

Answer 2

You can return promise from createFileReqInfo , then wait until it resolves

for (var i = 0; i < this.selectedItems().length; i++) {
    var row = this.selectedItems()[i];
    let info = await this.createFileReqInfo(row.Number(), FileRequestType.AssociatedDoc);
    fileReqInfo.push(info);
}

Or

for (var i = 0; i < this.selectedItems().length; i++) {
    var row = this.selectedItems()[i];
    this.createFileReqInfo(row.Number(), FileRequestType.AssociatedDoc)
       .then(info => {
               fileReqInfo.push(info);
            });

}

Where createFileReqInfo is defined as:

createFileReqInfo = (reportId: number, fileRequestType: FileRequestType) : Promise<any> => {
  return new Promise( (resolve, reject) => {
    let fileReq = new FileRequest(reportId, fileRequestType);
    var uCanView = false;
    this.reportModel.getReportSecurity(reportId).done((result) => {
        uCanView = result.CanViewReport;
        var info: {
            fileRequest: FileRequest,
            userCanView: boolean
        } = {
            fileRequest: fileReq,
            userCanView: uCanView
        }
        resolve(info);        
    });
    }
}