Cypress task fails and complains that task event has not been registered in the plugins file

Question

I am using the cypress cy.task() method/ function to copy a csv file from one directory to another directory. Below is my cy.task('copycsvFile') and relevant code written in support/index.js file. While running it throws following error; CypressError: cy.task('copycsvFile') failed with the following error: The 'task' event has not been registered in the plugins file. You must register it before using cy.task() Any idea why this is not recognised ?

Node version : v10.15.3, Cypress version : 3.1.5

//sample-spec.js file

cy.task('copycsvFile');

Below is my index.js file // support/index.js file

const fs = require('fs');

module.exports = (on) => {
    on('task', {
        copycsvFile: (Obj)=>{
          var fs = require('fs');
         fs.createReadStream('C:/Users/SomeName/Downloads/Export_Survey_CSV.csv').pipe(fs.createWriteStream('C:/User/Client/Client - Cypress Web UI Tests/cypress/fixtures/Export_Survey_CSV.csv'));
        }
    });
};

Answer 1

At last, I have figured out the answer.
I have added the below code in the wrong location and that was the reason it fails and returned the above error.
Now I have corrected the location and added under plugins/index.js and works perfectly.

I've also made a small change, ie I added return null since I didn't have anything to return in my case.

// In my spec file;

cy.task('copycsvFile');

// added below code under.. /plugins/index.js

const fs = require('fs');
    
module.exports = (on) => {
  on("task", {
    copycsvFile: (Obj) => {
      var fs = require("fs");
      fs.createReadStream(
        "C:/Users/SomeName/Downloads/Export_Survey_CSV.csv"
      ).pipe(
        fs.createWriteStream(
          "C:/User/Client/Client - Cypress Web UI Tests/cypress/fixtures/Export_Survey_CSV.csv"
        )
      );
      return null;
    },
  });
};