Simple Python collections.ChainMap-esque construct in JavaScript

chainmap.js

// The behaviour of Python's collections.ChainMap is the same as prototypal
// inheritance[1] in JavaScript:
//
// - Accessing a property of an object will traverse the prototype chain until
//   the property is found (or until the end of the chain); and
// - Assigning to a property will only mutate the first object in the prototype
//   chain (the object on which the property is being accessed).
//
// Thanks to this, we can implement something along the lines of Python's
// collections.ChainMap quite trivially.
//
// [1]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Inheritance_and_the_prototype_chain

export default function ChainMap(...maps) {
    if (!maps.length)
        return Object.create(null);
    const [m, ...ms] = maps;
    return Object.setPrototypeOf(m, chainmap(...ms));
}

export function newChild(m) {
    return Object.create(m);
}