How to load and execute external JavaScript file in Node.js with access to local variables?

To load and execute external JavaScript file in Node.js with access to local variables, we create a module with the variables and require the module.

For instance, we write

const PI = 3.14;

exports.area = (r) => {
  return PI * r * r;
};

exports.circumference = (r) => {
  return 2 * PI * r;
};

in circle.js to export the area and circumference functions.

Then we write

const circle = require("./circle");
console.log(circle.area(4));

to require the circle.js file and call the area function from circle.js.