Mimicking Named Parameters in JavaScript

Whilst working today I came across a test helper function that required a few too many parameters. Debating weather to break the function up, I decided that an elegant solution would be to take advantage of ES2015 object deconstruction and produce a form of ‘Named Parameters’. We all are very familiar with code in the past that looks like this:

const foo = (opts) => {
  opts = Object.assign({x: 10, y: 20}, opts);
  return `${x}, ${y}`;
};
foo({ x: 5 }) // 5, 20

Although it provides us with the public API that we desire, the internal implementation requires boilerplate that I feel takes away from the problem the function is trying to solve. However, with the introduction of ES2015 we are able to take advantage of object deconstruction and rewrite this code to be:

const foo = ({x=10, y=20}) => `${x}, ${y}`;
foo({ y: 15 }); // 10, 15

We can also produce dynamic default values based on other supplied inputs such as in this contrived example:

const foo = ({x=10, y=2*x}) => `${x}, ${y}`;
foo({ x: 4 }); // 4, 8