How to use function from self defined prototype - object.create

Question

I'm using object.create to create an object, based on a prototype I created.

This is the prototype

var employeePrototype = {
            calulateTax: function() {
                console.log(salary * taxRate);
            }
        };

This is the object I created.

var jack = Object.create(employeePrototype);
        jack.salary = 25000;
        jack.taxRate = .40;
        jack.calulateTax();

When I call jack.calculateTax, I get the following error

index.html:14 Uncaught ReferenceError: salary is not defined at Object.calulateTax

Eddie · Accepted Answer · 2019-05-10 17:38:10Z

2

You have to use this to use the salary and taxRate of the instance

var employeePrototype = {
  calulateTax: function() {
    console.log(this.salary * this.taxRate);
  }
};

var jack = Object.create(employeePrototype);
jack.salary = 25000;
jack.taxRate = .40;
jack.calulateTax();

answered May 10, 2019 at 17:38

Eddie

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Comments

Patrick Roberts · Accepted Answer · 2019-05-10 17:48:04Z

0

Instead of using Object.create(), it's a lot more orthodox to use a class. Here's how you'd accomplish it using one:

class Employee {
  salary = 25000;
  taxRate = .40;

  calulateTax () {
    console.log(this.salary * this.taxRate);
  }
}

const jack = new Employee();

jack.calulateTax();

The class fields are part of TC39/proposal-class-fields, which is in stage 3, but is already part of Chrome, Firefox, and Node.js, or can be transpiled using Babel.

For ES2015 support, you can simply move the initialization into the constructor:

class Employee {
  constructor () {
    this.salary = 25000;
    this.taxRate = .40;
  }

  calulateTax () {
    console.log(this.salary * this.taxRate);
  }
}

const jack = new Employee();

jack.calulateTax();

answered May 10, 2019 at 17:48

Patrick Roberts

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1 Comment

user11341032 Over a year ago

Thank you, and I appreciate it. I'm just going through a course atm, so this is how they do it. ES6 and stuff is coming up soon.

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