Angular / Electron service output passed to variable but returning undefined

Question

I have a service and when I run the code labeled #1 it returns to data in the console but when I assign it to a variable I get undefined.

Here is the code:

In the Service:

executeShell(command) {
exec(command, (error, stdout, stderr) => {
  if (error) {
    return stderr;
  } else {
    return stdout;
  }
});
}

In the component.ts:

output: any; // define the variable

Then if I run #1 below:

this.electronService.executeShell('ls'); // #1

the output on the console is corrent.

But If I try this:

this.output = this.electronService.executeShell('ls'); // #2
console.log(this.output); // #2

I get undefined

My issue is that #1 returns the list in the console but #2 is returning undefined.

How can I fix this?

score 1 · Accepted Answer · answered Jun 19 '20 at 11:50

The value is returned from a callback, so it's asynchronous. You might have to return an observable/promise to capture the data. Try the following

Service

executeShell(command) {
  let result = new BehaviorSubject<any>(null);
  exec(command, (error, stdout, stderr) => {
    if (error) {
      result.error(stderr);
    } else {
      result.next(stdout);
    }
  });
  return result.asObservable();
}

Now subscribe in the component to get the notification.

Component

this.electronService.executeShell('ls').subscribe(
  response => {
    if(response) {   // <-- default value of the observable is `null`
      this.output = response;
    }
  },
  error => {
    this.output = error;
  }
);

Angular / Electron service output passed to variable but returning undefined

1 Answers1