Facies

facies is a featureful parameters signature module for nodejs.

Features

• Duck type matching
• Default values

See the changelog and the API reference

Requirements

facies works with NodeJS 6.x and above. Install it the usual way:

npm install facies

How To

facies is designed for use with array-like values, e.g. the arguments keyword:

const facies = require("facies");

const target = function () {
	const parameters = facies.match([
		Number,
		[String, "a"],
	], arguments);

	// parameters is an array:
	// - [0] is a Number
	// - [1] is a string with default value "a"
};

It works by matching the given values against a list of interface definitions. Interface definitions are constructed either from a type constructor for exact matching or from a literal object describing the expected interface. So both String and {length: Function} will match strings.

Interface definitions can be given in an array where the last value will be the default value used if none of the other values match the corresponding value. Multiple interface definitions can also be bundled together using the variadic Interface construct, which responds to the instanceof operator:

[]         instanceof facies.Interface({forEach: Function}); // true
new Map()  instanceof facies.Interface({forEach: Function}); // true
/^$/       instanceof facies.Interface(RegExp, Date);        // true
new Date() instanceof facies.Interface(RegExp, Date);        // true

If actual values do not match the expected interface definition, facies.match will also throw a TypeError. If more values are given than the result of matching (including default values), facies.match will also throw a TypeError.

The facies.match function is currified using Ramda, so that it can be partially applied to the interface expectation if needed.