invocation-list v0.1.3

Invocation Lists

This is a small library that can be used with ES7/TypeScript decorators. It lets you specify that a function should be executed when another one is executed. You can do this multiple times, creating invocation lists under a single function that are inherited using standard JavaScript prototype inheritance.

Here is how it looks like in practice:

import {invokedBy} from 'invocation-list';
let a = "";
class Example {
	
	hello() {
		a += "0";
	}

	@invokedBy('hello');
	method1() {
		a+= "1";
	}
	
	@invokedBy('hello')
	method2() {
		a+= "2"
	}
}

let example = new Example();
example.hello();
expect(a).toBe("012");

In the above example, method1 and method2 were added to the 'invocation list' of hello, which includes the body of the original method at the beginning.

This plays well with JavaScript prototype inheritance.

class Derived extends Example {
	@invokedBy('hello');
	method3() {
		a += "3";
	}
}

The above modifies the invocation list for hello only for objects of Derived.

However, note that if you override the managed method in a more derived prototype:

class Derived extends Example {
	hello() {

	}
}

The member is no longer managed by the invocation list of less-derived prototypes and they don't interfere with the new functionality.

Now, you can keep using invokedBy on that member, but overriding hello essentially blocked off the older invocation lists.

class Derived extends Example {
	hello() {
		a += "0";
	}
	@invokedBy('hello')
	method4() {
		a += "4";
	}
}
new Derived().hello();
expect(a).toBe("04");

Things would've been okay if we'd added a super call:

class Derived extends Example {
	hello() {
		super.hello();
	}
	@invokedBy('hello')
	method4() {
		a += "4";
	}
}
new Derived().hello();
expect(a).toBe("01234");

Motivation

The motivation of this library is to allow syntax like this when working with React:

class ExampleComponent extends React.Component {
	@Lifecycle.componentWillUpdate
	@Lifecycle.componentWillMount
	doStuff() {
	}
}

This is implemented in another library.