Value of a variable to be read asynchronously

Question

I read value from registry and set value from registry to variable in my code. I see fetching the value from registry is happening asynchronously.

I am regedit package from node. I have tried setTimeout for constructENVTable, but it didn't work. Please note:mainfunc() is triggered from html page body onload

//declared globally
var regValue = "";

function mainfunc() {
  setRegistryValueForFirstTime();
  constructENVTable();
}

function setRegistryValueForFirstTime() {
  let path = "HKLM\\....\\Environment";
  regedit.list('HKLM\\...\\Environment', function(err, result) {
    try {
      regValue = result[path].values.XYZ.value;
      alert(regValue); //prints value correctly
      app.console.log("Registry value for ANSYS_LI is  already set");
    } catch (err) {
      app.console.log(err);
      app.console.log("setting up registry value");
      setRegistryValue();
    }
    alert(regValue); //doesn't print value
  });
}

  function constructENVTable() {
    alert(regValue); //doesn't print value
  }

Answer 1

You can wrap regValue with a Promise:

var regValue;

function mainfunc() {
    setRegistryValueForFirstTime();
    constructENVTable();
}

function setRegistryValueForFirstTime() {
    let path = "HKLM\\....\\Environment";
    regedit.list('HKLM\\...\\Environment', function (err, result) {
        try {
            regValue = new Promise(
                (resolve, reject) => resolve(result[path].values.XYZ.value)
            )

            app.console.log("Registry value for ANSYS_LI is  already set");
        } catch (err) {
            app.console.log(err);
            app.console.log("setting up registry value");
            setRegistryValue();
        }
        alert(regValue); //doesn't print value
    });
}

function constructENVTable() {
    // alert(regValue); //doesn't print value
    regValue.then(
        value => alert(value)
    )
}