how to store array from database in variable in javascript

Question

I'm new to javascript and want to store (array) value from database in variable which I can manipulate later in my code. I'm using MongoDB and this is one example of the objects that are stored.

{
    "_id": {
        "$oid": "60a2247fcfe6fbbd6ce93ee0"
    },
    "project": ["4", "1"],
    "title": "Test",
    "url": "test",
    "urlTitle": "test1",
    "urlInstance": "https://www.google.com/",
    "__v": 0
}

I want to store the project values in an array (x). I use this code.. I figure out that myFunction() in not returning anything that's why in the console I get "x=undefined". what should I change in the code so the function return the value of the project? Thank you in advance.

function myFunction() {
  User.find({title: "Test"})
  .then(
    (myData) => {
    var rez=  myData[3].project;  
    return rez; 
  })

}

var x= new Array;
x= myFunction();
console.log ("x=" + x);

fravolt · Accepted Answer · 2021-05-17 11:44:33Z

1

I think this is related to database find operations being asynchronous, meaning they do not return immediately, but need some time to do so. Take a look at this documentation page for some more info.

Have you tried console.log-ing rez before returning it? You should see that it prints the result, but it happens after x=undefined is printed. In other words, myFunction is not waiting for the database retrieval to finish before returning.

Concretely, you'll want to await the result of your database retrieval.

async function myFunction() {
  // await here prevents the code from continuing before a result has been obtained
  let myData = await User.find({title: "Test"});

  let rez = myData[3].project;
  return rez;
}

async function retrieveData() {
  let x = await myFunction();
  console.log("x=" + x);
}

retrieveData();

answered May 17, 2021 at 11:44

fravolt

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3 Comments

tanja_a Over a year ago

Thanks for the answer, but when I try to use your code I get error "Unhandled error: TypeError: Cannot read property 'project' of undefined at myFunction"

fravolt Over a year ago

Have you tried adding console.log(rez) before return rez in your own code? Does that work and print the correct result?

tanja_a Over a year ago

I tried that but it not work (not printing anything) and still the same error.

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