cannot find the name "module"

I am trying to run a simple typescript file where I am exporting a function named sum as shown below:

I am writing node script.

function sum(a:number):number{
  return a;
}
module.exports.sum=sum;

I don't understand what I did wrong.

I wrote this simple script to understand the unit test case. I thought if this file is running properly then i will go and start basic test case using mocha and chai.

below is my test code:

"use strict"

// Import chai.
let chai = require('chai'),
    path = require('path');

chai.should();

let SampleTest = require(path.join(__dirname, '..', 'sample.js'));

describe('Sampletesting', () => {
    describe('function sum', function(){
        it('should return number', function(){
            sum(1).should.equal(1);
        })
    })
});