Multi tool use

Return type in asynchronous function using mongoose produces error

I am getting an error while trying to compile the following code:

public getCompanies(): Array<ICompany>{
Company.find({}, (err, data)=>{
if (err) console.log(err);
let companyArray = new Array();
for (let company of data){
companyArray.push(company);
}
return companyArray;
});
}


There is an error with the return type of the function: error TS2355: A function whose declared type is neither 'void' nor 'any' must return a value.

Got the same error using then/catch functions.

Is there a way to make this work without converting the return type to any?

Thank you in advance

1 Answer
1

The compiler is right about your function not actually returning any value.

The problem is that Company.find takes a callback which is executed at a later date when the requested query competes. So everything you write after (err, data)=>{ will get not get executed when you call getCompanies, and the return you have is not a return from getCompanies, but rather a return from an anonymous function that get executed later.

Company.find

(err, data)=>{

getCompanies

return

getCompanies

You can either use a similar approach (passing in a callback) to be notified of when the query completes:

class foo {
public getCompanies(onCompleted: (data: ICompany)=> void): void{
Company.find({}, (err, data)=>{
if (err) console.log(err);
let companyArray = new Array();
for (let company of data){
companyArray.push(company);
}
onCompleted(companyArray);
});
}

public usage(){
this.getCompanies(data=>
{
console.log(data);
})
}
}


Or you can just return the DocumentQuery that find returns and use then or async/await to get the result:

DocumentQuery

find

then

async/await

class foo {
public getCompanies() {
return Company.find({}, (err, data)=>{
if (err) {
console.log(err);
}
let companyArray = new Array();
for (let company of data){
companyArray.push(company);
}
});
}
public async usageAsync(){
let data = await this.getCompanies();
console.log(data);
}

public usage(){
this.getCompanies()
.then (data=>
{
console.log(data);
})
}
}


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