How to fix variable is not defined` - The variable in question is clearly defined in my code

Question

Hey amazing people of the Internet, Pretty noobish question here, but I'm having a bit of a problem with some of this Javascript I wrote. Here's the code -

const req0 = http.request({
      hostname: `api.trello.com`,
      port: 443,
      path: `/1/lists/5cb77e9ef180dd2bbb25acf2/cards?key=${trelloKey}&token=${trelloToken}&fields=name`,
      method: `GET`
    }, res => {
      let str = '';
      res.on('data', chunk => {
        str += chunk;
      });
      res.on('end', () => {
        try {
            var level0Data = JSON.parse(str);
            console.log(`Level 0: ${level0Data}`)
            level0Data.forEach((k,v) => {
                var id = k.id;
                var name = k.name;
                console.log(`${id} = ${name}`);
            });
        } catch(error) {
            console.log(error);
        }
      });
    });
    req0.on('error', error => {
      console.log(error);
    });
    req0.end();


  level0Data.forEach(function(level0Names) {
    // code here
  });

The issue I'm having with this is that it keeps giving me an error stating that the level0Data is not defined. I know it's a pretty newbie question, but I'd appreciate some guidance with it. Thanks!

Answer 1

Do you see that level0Data is not defined in below scope? (MDN reference(Scope))

  level0Data.forEach(function(level0Names) {
    // code here
  });

You must use level0data inside of callback function.

// NOTE: Level0data is available only here, as you defined in this scope.
...

            var level0Data = JSON.parse(str);
            console.log(`Level 0: ${level0Data}`)
            level0Data.forEach((k,v) => {
                var id = k.id;
                var name = k.name;
                console.log(`${id} = ${name}`);
            });

...

Or you can pass a function to handle callback.

function handle(str) {
            var level0Data = JSON.parse(str);
            console.log(`Level 0: ${level0Data}`)
            level0Data.forEach((k,v) => {
                var id = k.id;
                var name = k.name;
                console.log(`${id} = ${name}`);
            });

  level0Data.forEach(function(level0Names) {
    // code here
  });
}

...

try {
  handle(str)
} catch(e) {
  console.error(e)
}