LoanJS

Super small (~500B) and fast module to calculate loan in js (browser/node.js) for equal/decreasing/annuity/annuityDue installments, the sum of interest, etc, with TypeScript support

Getting Started

Install with:

npm install loanjs

Calculating Loan:

import { Loan } from 'loanjs';
// or
const { Loan } = require('loanjs');

const loan = new Loan(
  1000, // amount
  12,   // installments number
  5,    // interest rate
  'annuity'  // loanType: 'annuity' | 'annuityDue' | 'diminishing' | GetNextInstalmentPartFunction
);
/** returns
{
  installments  : [
    {
      capital     : number,
      interest    : number,
      installment : number,
      remain      : number
    },
    //...
  ],
  amount        : number,
  interestSum   : number,
  capitalSum    : number,
  sum           : number
}
*/

Documentation

Loan

LoanJS.Loan(amount, installmentsNumber, interestRate, loanType)

Arguments

| Argument | type | default | Description | ------------------ | -------------- | --------- | ------------------ | amount | number | *required | full amount of Loan | installmentsNumber | number | *required | how many installments will be (in months) | interestRate | number | *required | interest rate in percent (ex. 3.5) | loanType | string or fn | annuity | annuity | annuityDue | diminishing | GetNextInstalmentPartFunction

interface InstallmentPart {
  capital: number;
  interest: number;
  installment: number;
}

type GetNextInstalmentPartFunction = (
  amount: number,
  installmentsNumber: number,
  interestRateMonth: number,
  capitalSum: number
) => InstallmentPart;

Returns

{
  installments  : [
    {
      capital     : number,
      interest    : number,
      installment : number,
      remain      : number
    }
  ],
  amount        : number,
  interestSum   : number,
  capitalSum    : number,
  sum           : number
}

Examples

typescript example

import { Loan } from 'loanjs';

const annuityLoan = new Loan(1000, 12, 5, 'annuity');

const annuityDueLoan = new Loan(1000, 12, 5, 'annuityDue');

const diminishingLoan = new Loan(1000, 12, 5, 'diminishing');

const customInstalmentLoan = new Loan(1000, 12, 5, getNext10Instalment);
function getNext10Instalment (amount: number, installmentsNumber: number, capitalSum: number, interestRateMonth: number) {
  const capital = rnd(amount / installmentsNumber);
  const interest = 10;
  const installment = capital + interest;

  return { capital, interest, installment };
}

nodejs example

import { Loan } from 'loanjs';
// or
const { Loan } = require('loanjs');

const loan_1 = new Loan(1000, 12, 5, 'diminishing');
// loan on 1 000($) in 12 loanType installments (ex. months) with 5% interest rate

const loan_2 = new Loan(500000, 360, 3.5, 'annuity');
// loan on 500 000($) in 360 equal installments (30 years) with 3.5% interest rate

Browser example:

You can also render loan as html table

<script src="../../dist/loan.js"></script>
<script src="../../dist/loanToHtmlTable.js"></script>
<script>
    const loan = new LoanJS.Loan(1000, 12, 5, 'annuity');

    const div = document.createElement("div");
    div.innerHTML = LoanJS.loanToHtmlTable(loan); // loan rendering as html table string
    document.body.appendChild(div);
</script>

more examples here

Similar projects

• InterestJS - counting regular savings

Contributing

Im open for contributors :).

Release History

2023-07-25 v1.1.0

• add annuityDue interest rate loan type
• changing the fourth argument diminishing to loanType (annuity | diminishing | annuityDue), with backward compatibility (false == 'annuity', true == 'diminishing')
• refactor getNextInstalment to be open for extensions
• add option to provide function to loanType to customize instalments counting

2023-06-23 v1.0.11

• add TypeScript types
• code cleanup
• packages update

2017-08-06 v1.0.0

• go to es6
• make dist files
• make 100% covered tests

2016-02-29 v0.1.4

• update dependencies

2015-10-12 v0.1.3

• fixing typo intrest -> interest #3
• update dependencies

2014-11-10 v0.0.4

• update dependencies

2014-11-10 v0.0.2

• now you can use it in node/browserify and browser

License

Copyright (c) 2023 Grzegorz Klimek Licensed under the MIT license.