How to get current user ID from backend function and use it in a client-side query in Velo?

In Velo, I am trying to compare the owner ID of already created posts with the ID of current logged-in user.

For this, I want to recall a back-end function that produces the current user ID ("_owner") in use it in a client-side query function. I have been just exhausted of retrieving the "_owner", which I am going to use in the query function, correctly. I know from console.log(memberId) I get the ID inside the query function, but I'm not able to use it as value for the the query function. Any help please?

In the back-end side I have this code:

import { currentMember } from 'wix-members-backend';

export function myGetCurrentMemberFunction() {
 return currentMember.getMember()
    .then((member) => {
        const memberId = member._id;
        return memberId;
    })

}

In the client-side I have this code:

import { myGetCurrentMemberFunction } from 'backend/backendfunctions.jsw'

function matchPostCurrentUser(event) {
// Matching current user ID with that of the entered post ID

wixData.query("Collection1")
    .eq("_owner", myGetCurrentMemberFunction()
    .then(memberId => {
        console.log(memberId)
         memberId
    })
    )
    .find()
    .then((results) => {
        let result = results.items
        console.log(result)
        if (results.items.length === 0) {
            console.log("You choosed other users post's ID" + result )               
        }
    })

}

Look like you've made a bit of a mess of your client-side code. The easiest, and probably most readable way to do this is using async/await instead of .then with the promises.

That would look something like this:

async function matchPostCurrentUser(event) {
  const currentMemberId = await myGetCurrentMemberFunction();
  const results = await wixData.query("Collection1")
    .eq("_owner", currentMemberId)
    .find();

  console.log(results.items);
  
  // etc...   
}

If you really want to use .then, it would look something like this:

function matchPostCurrentUser(event) {
  myGetCurrentMemberFunction()
    .then(memberId => {
         return wixData.query("Collection1")
           .eq("_owner", memberId)
           .find();
    })
    .then((results) => {
      let result = results.items;
      console.log(result);
      if (results.items.length === 0) {
        console.log("You choosed other users post's ID" + result );               
      }
    });
}