Please I am trying to concatenate string result to a variable in an express router but it returns an empty string - arrays

Question

I am trying to iterate through the array get the value and search the database, then concatenate the database result to the string translation
app.get('/translate',function(req,res) {
let translate = '';
['hello','love'].forEach(async (word) => {
let trans = await
NaijaLang.find({"engword": word, "naijalang": "yoruba"});
translate +=" " + trans[0].translation;
//Returns values
console.log(translate)
});
//Returns Empty String;
console.log(translate)
res.send(translate);
});

Answer 1

Because you do some async stuff there, but you send the value synchronously. Basically, this code will run in this order:
run let translate='';
run ['hello','love'].forEach(...)
run await NaijaLang.find(...) asynchronously for word=hello
run await NaijaLang.find(...) asynchronously for word=love
run console.log(translate) and res.send(translate);
resolve the value of await NaijaLang.find(...) -> this is the time when the translate is updated for the first time (either for word=hello or word=love. Whatever finishes earlier)
resolve the value of second call await NaijaLang.find(...) -> this is the time when the translate is updated for the second time. But the value was already send in the 5th step.
You can find more detailed explanation here: https://blog.lavrton.com/javascript-loops-how-to-handle-async-await-6252dd3c795
And you can also find there how to fix it. You can use the for-of loop instead of forEach:
app.get('/translate',function(req,res){
let translate='';
for (let word of ['hello','love']) {
let trans=await NaijaLang.find({"engword":word,"naijalang":"yoruba"});
translate+=" " + trans[0].translation;
//Returns values
console.log(translate)
}
//Returns Empty String;
console.log(translate)
res.send(translate);
});
This time, the code will execute as you probably want. First, the find method will be called for word=hello, then, after the execution is finished, the find method will be called for word=love and finally after both calls are finished, the res.send will be called.