Composable-js NPM

Composable-js

Use cases

This package enables programmer to not care about the order of referencing and overriding decorators for constructors and methods.

In following example the result of the console.log will be 1.

let a: any;

function referencingDecorator(object: any, propertyName: string, descriptor: PropertyDescriptor) {
    a = descriptor.value;
}

function overridingDecorator(object: any, propertyName: string, descriptor: PropertyDescriptor) {
    descriptor.value = (...args: any[]) => 1;
}

class ExampleClassA {
    @referencingDecorator
    @overridingDecorator
    exampleMethod() {
        return 0;
    }
}

console.log(a());

On the other hand, if we swap the order of the decorators, we get 0.

//...
@overridingDecorator
@referencingDecorator
exampleMethod()
{
    return 0;
}

//...

This happens because of a being a reference of the original function, not the overridden one. Same principle applies to constructors.

Composable-js aims to solve this problem.

let a: any;

function referencingDecorator(originalFunction: Function, composedFunction: Function) {
    a = composedFunction;
    return originalFunction
}

function overridingDecorator() {
    return (...args: any[]) => 1;
}

class ExampleClassA {
    @ComposableFunction.decorator(referencingDecorator)
    @ComposableFunction.decorator(overridingDecorator)
    exampleMethod() {
        return 0;
    }
}
console.log(a());

class ExampleClassB {
    @ComposableFunction.decorator(overridingDecorator)
    @ComposableFunction.decorator(referencingDecorator)
    exampleMethod() {
        return 0;
    }
}


console.log(a());

Using the composable function API the order of decorators is negated in terms for referencing. a will always call the final function, not the intermediary.

Usage

Composable-js exposes to APIs - ComposableClass and ComposableFunction.

static decorator<T>(transformation:(original:T,composed:T) => T) method allows easy decorator creation by providing a transformation function, where T is either a constructor or a function.

You can also use the direct method of getting instance of ComposableClass or ComposableFunction assigned to particular constructor or function by calling get<T>(value:T). The returned instance of the class has composed property which is the current version of the overridden function and chain<T>(transformation:(original:T,composed:T) => T) which allows for manual chaining.