interfaces.js

Brings interfaces to JavaScript

/* quick-and-dirty */
const Types = {
	string: x => typeof x == "string",
	number: x => typeof x == "number"
};

const Interface = model => {
	const check = scope => {
		let fails = 0;

		Object.keys(model).forEach(prop => {
			if(scope[prop] === undefined) {
				console.error(`${prop}: field is required`);
				++fails;
			}
		});
		return fails;
	};

	const newscope = () => {
		return new Proxy({}, {
			set(target, prop, value) {
				const type = model[prop];
				const typecheck = type ? Types[type] : null;

				if(type) {
					if(!typecheck)
						console.warn(`${type}: unknown type`);
					else if(!typecheck(value))
						console.error(`${prop}: expect a ${type}`);
				}
				target[prop] = value;
				return true;
			}
		});
	};

	const concretizes = fn => {
		const scope = newscope();

		fn(scope);
		return check(scope) ? null : scope;
	}

	return concretizes;
}

Example usage

const ShapeInterface = Interface({
	base: "number",
	height: "number"
});

/* direct */
const Triangle = ShapeInterface(self => {
	self.base = 2;
	self.height = 5;
	self.calculateArea = () => (self.base * self.height) / 2;
});
console.log("Triangle", Triangle.calculateArea());

/* instance */
function InstanceTriangle(base, height) {
	return ShapeInterface(self => {
		self.base = base;
		self.height = height;
		self.calculateArea = () => (self.base * self.height) / 2;
	});
}
const it = new InstanceTriangle(5,5); /* new is optional */
console.log("InstanceTriangle", it.calculateArea());

/* automatic instance */
const AutoTriangle = (base, height) => ShapeInterface(self => {
	self.base = base;
	self.height = height;
	self.calculateArea = () => (self.base * self.height) / 2;
});
const at = AutoTriangle(3,3);
console.log("AutoTriangle", at.calculateArea());

/* class */
class TriangleClass {
	constructor(base, height) {
		this.base = base;
		this.height = height;
		ShapeInterface(self => Object.assign(self, this));
	}

	calculateArea() {
		return (this.base * this.height) / 2;
	}
}
const tc = new TriangleClass(5,6);
console.log("TriangleClass", tc.calculateArea());