TypeError: callback is not a function in Node.js

Question

I am learning node.js and below is my code for the same

app.js :

const forecastService  = require('./forecast')

forecastService('New York', (error,data) => {

    if(error){
        console.log('Error in getWeatherForecast ')
    }else {
        console.log('data '+data)
    }
})

forecast.js :

const request  = require('request')

const getWeatherForecast = (city,callback) => {

    console.log('printing typeof callback ..'+typeof callback) 
    // prints function 
    console.log('printing callback ..'+callback)
    //prints actual function definition 

    const api = 'http://api.weatherstack.com/current?access_key=abcdefghijklmn'

    const weather_url = api + '&request='+city
    request({url:weather_url, json:true} , (error,response,callback) => {

        if(error){       
            callback('unable to connect to weather service',undefined)
        }else (response.body.error){
            const errMessage = 'Error in Response :'+response.body.error.info 
            console.log(errMessage)
            callback(errMessage,undefined) // getting error here 
        }
    }) 
}

module.exports = getWeatherForecast

Issue :

In forecast.js , at line callback(errMessage,undefined) , I am getting error - TypeError: callback is not a function

I have also printed callback in forecast.js as typeof callback = function and callback = actul function definition

But I am still not getting ay clue what is the error .

Can anybody please help ?

I have gone through public posts like TypeError : callback is not a function where all is saying callback is not passed correctly as a parameter which seems NOT the case with me

eol · Accepted Answer · 2020-06-09 07:23:53Z

The problem is that your request-callback definition is wrong. According to the docs

The callback argument gets 3 arguments:

An error when applicable (usually from http.ClientRequest object)

An http.IncomingMessage object (Response object)

The third is the response body (String or Buffer, or JSON object if the json option is supplied)

So obviously the third paramter is not a function and in fact you're shadowing the callback from the outer scope. You can fix this problem by simply removing the third paramter:

request({url:weather_url, json:true} , (error,response) => {

        if(error){       
            callback('unable to connect to weather service',undefined)
        }else if (response.body.error){
            const errMessage = 'Error in Response :'+response.body.error.info 
            console.log(errMessage)
            callback(errMessage,undefined) // getting error here 
        } else {
           // handle success
           callback(undefined, response.body);
        }
})

A word of advice - you should use Promises and async/await instead of callbacks as it greatly increases the readability and the flow of your code.

Collectives™ on Stack Overflow

TypeError: callback is not a function in Node.js

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related