JSD > Project: Build a Slackbot > Tutorial > Step 14: Handle Errors Gracefully

Step 14: Handle Errors Gracefully

If you try the pass an invalid city name to your /weather slash command, we’ll receive the following error in our server log:

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This is happening because we aren’t appropriately handling errors. In an ideal scenario, if a user was to pass an invalid city name to the /weather slash command our server should respond back a message informing users of the error

1. Update `openWeatherApi()` in `index.js`

Update the openWeatherApi() to reflect the code below:

async function openWeatherApi (query) {
  try {
    const url = 'https://api.openweathermap.org/data/2.5/weather'
    const apiKey = process.env.OPEN_WEATHER_API_KEY

    // make api request using axios
    const response = await axios.get(url, {
      params: {
        appid: apiKey,
        q: query,
        units: 'imperial'
      }
    })

    console.log(response)
    return response.data
  } catch (e) {
    console.log(e)

    // "throw" error, which will be "caught"
    // by the function that called openWeatherApi
    throw new Error('City not found')
  }
}

Here’s a summary of the update:

In the catch(){} part of our try..catch block we are using throw to forward our error to the function that called openWeatherApi() - we are doing this because we want to make the app.post(/weather...) route handler aware that an error occurred during our API request to OpenWeather
We are following the JavaScript best practice of creating an Error object (using the new keyword) when constructing errors; we are passing a message to provide additional context around the error

2. Update `app.post(/weather...)` in `index.js`

Now that we’ve made openWeatherApi() throw any errors it encounters, our app.post(/weather...) route handle with then catch those errors in its own try..catch block`

Update the app.post(/weather...) to reflect the code below:

app.post('/weather', async (req, res) => {
  try {
    console.log(req.body)

    // respond with an OK to sender within 3 secs
    // as required by Slack for delayed responses
    // documentation: https://api.slack.com/slash-commands#responding_response_url
    res.json()

    // extract city passed in as a parameter to
    // our slash command (/weather cityName)
    const query = req.body.text

    // making API request via openWeatherApi function
    const response = await openWeatherApi(query)

    // print out OpenWeather API
    // response to the console
    console.log(response)

    // Create a forecast based on info
    // received from OpenWeather
    const forecast =
      `Current temperature in ${query} is ${response.main.temp} degrees with a high of ${response.main.temp_max} degrees and a low of ${response.main.temp_min} degrees`

    // construct an object (according to Slack API docs)
    // that will be used to send a response
    // back to Slack
    const data = {
      'response_type': 'in_channel',
      'text': forecast
    }

    // make a POST request (with axios) using "response_url"
    // to complete our "delayed response" as
    // per the Slack API docs
    axios.post(req.body.response_url, data)

    // res.json(data)
  } catch (e) {
    console.log(e)

    // construct an error response to send
    // to Slack in the case of the user
    // sending an invalid city

    const errorResponse = {
      'response_type': 'in_channel',
      'text': '[ADD ANY SLACK EMOJI CODE HERE] Oh oh, there was a problem with your last request. Please make sure you enter a valid city name.'
    }

    axios.post(req.body.response_url, errorResponse)
  }
})

Here’s a summary of the update:

In the catch(){} portion of openWeatherApi() we are constructing an object that will contain our response to Slack (structure of this object is based on Slack API docs); in the "text" section of the object, we are sending a helpful message to users so they can take corrective action
Lastly, we’re using axios to make a POST request to the response_url and send the errorResponse object that contains our message

3. Try your `/weather` slash command with an invalid city name

Restart your Express server and go back to your development workspace on Slack and try the /weather slash command with an invalid city name such as /weather yolo town
After submitting the slash command with an invalid city), an informative error message should be displayed in Slack

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Step 14: Handle Errors Gracefully