Angular CLI strict mode

constants.js

// constants.js
export const PI = 3.14159265357989;

index.js

// index.js
import { add } from './utils';
const subtract = (a, b) => a - b;

console.log(add(1, 2));

operations.js

// operations.js
export const add = (a, b) => a + b;
export const subtract = (a, b) => a - b;

utils.js

// utils.js
export * from './operations';
export * from './constants';