CODEWITHSUNDEEP
node.jsecmascript-6node-moduleses6-class
NicklasN
NicklasN

Reputation: 484

Calling a local method inside a class in Node.js and module.export

So I have a class with functions where one is dependent on another. This class is exported with module. According to anything I can find I should be able to use "this" but that throws an error.

Example: 

class Test{

  test(){
    console.log('hello');
  }

  dependentMethod(){
    this.test();
  }
}

module.exports = Test;

This however throws these errors in node: 

(node:69278) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): TypeError: Cannot read property 'test' of undefined
(node:69278) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
(node:69278) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 2): TypeError: Cannot read property 'test' of undefined

It will work fine if I put the function outside the class though. Can anyone explain why this fails? :)

EDIT:

This is the code in server.js (simplified for the example) that uses the class: 

const test = require(__dirname + '/server/Test');


const validator = async function(req, res, next){

    const test = new test();
    const serverTest = await test.dependentMethod();
    next();

};

app.get('/Response/:id/:is/:userId/:hash', validator, async function (req, res, next) {
   //does smth
}

Used seperately does not work either

const test = new Test();

app.get('/Response/:id/:is/:userId/:hash', Test.dependentMethod, async function (req, res, next) {
     //Same error
}

Upvotes: 0

Views: 9516

Answers (3)

Rahul Somaraj
Rahul Somaraj

Reputation: 277

 class Test{

   test(){
    console.log('hello');
   }

   let dependentMethod = ()=>{
     this.test();
   }
  }

 module.exports = Test;

either manually bind this or use arrow functions which will bind this to the class object

Upvotes: 3

Enthusiastic Developer
Enthusiastic Developer

Reputation: 762

Man, you're not showing you real code to us.

I feel that in real life you are using test.dependentMethod as middleware. And it aclually is using standalone function loosing the context. Thats's why you have an error Cannot read property 'test' of undefined.

The solution is either using test.dependentMethod.bind(test) or the code from your Edit section, where you created separate validator function and using class instances correctly.

Upvotes: 1

Hardik Shah
Hardik Shah

Reputation: 4200

Working as expected.

Take a look here. You just need to rectify some syntactic errors.

Test.js

class Test{

  test(){
    console.log('hello');
  }

  dependentMethod(){
    this.test();
  }
}

module.exports = Test;

Test1.js

const fileR = require('./Test.js');

const validator = async function(){

 const fr = new fileR();
 const serverTest = await fr.dependentMethod();

};

validator();

Output:

> hello

Upvotes: 6

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