Atween

Hooking into Business Logic

• Install

• Usage

• Concepts

  • Interceptors
  • Hooks
  • Events

• API

  • registerInterceptor(case, config)
  • runInterceptors(case, input, [context])
  • registerHook(case, config)
  • runHooks(case, input, [context])
  • registerEvent(case, config)
  • runEvents(case, input, [context])

Lead Maintainer: Christian Blaschke / @platdesign

Install

npm install --save atween

Usage

const Atween = require('atween');
const atween = new Atween();

Concepts

Interceptors

Basically an interceptor transforms a given input an returns it. If there are multiple interceptors registered on the same case they will get the result of its antecessor as input. Additionally they will get the original-input as second parameter. If an error occurs inside of an interceptor the error object will be decorated with $prevResult and $input. Interceptors run sequentially based on their priority and can return a Promise if transformation needs async operations. If an interceptor does not return a value (or s.th. like null or undefined) it will pipe through its input value. Interceptor methods can have an execution context (this).

Methods

• registerInterceptor(case, config)
• runInterceptors(case, input, [context])

registerInterceptor(case, config)

• case - (String) Name of the case as a string.

• config - (Object|Function)

  If given config is a function it will be used as handler.

  • priority - (Number) Give a priority to influence execution order. (Default: 1000)
  • handler(prevResult, originalInput) The "transform"-logic function.

atween.registerInterceptor('myUseCase', {
    priority: 500,
    handler: function(prevResult, originalInput) {
        return prevResult + 1;
    }
});

or without specific priority:

atween.registerInterceptor('myUseCase', function(prevResult, originalInput) {
    return prevResult + 1;
});

runInterceptors(case, input, [context])

Returns a Promise which resolves with the result of the last executed interceptor-handler. In case of an error it rejects with an error having two additional attribtues: $prevResult and $input.

• case - (String) Name of the case as a string.
• input - Every input which should run through the chain of registered interceptors.
• context - (Object) Give a specific object which will be used as execution context of each handler.

atween.registerInterceptor('myUseCase', {
    priority: 500, // Default is 1000
    handler: function(prevResult, originalInput) {
        return prevResult + 1;
    }
});
// result: 5 + 1 = 6
 
atween.registerInterceptor('myUseCase', {
    // Will run with default priority of 1000
    handler: function(prevResult, originalInput) {
        return prevResult + originalInput;
    }
});
// result: 6 + 5 = 11
 
atween.registerInterceptor('myUseCase', {
    priority: 1500,
    handler: function(prevResult, originalInput) {
        return prevResult * this.factor;
    }
});
// result: 11 * 2 = 22
 
atween.runInterceptors('myUseCase', 5, { factor: 2 })
    .then((res) => expect(res).to.equal(22));

Hooks

Hooks can be registered on a specific case with a unique name. Running a case with multiple hooks registered on it will execute all hook-handlers sequentially by priority. The first parameter passed into each hook-handler is the input given by the executor. Its result will be stored on a result-object with given name as key. The result-object is passed into each hook-handler as second paramter. If all hook-handlers of a case run successfully the result-object will be returned. Hook-handlers can return a Promise to do async stuff. A hook without a name will ignore the return value except its a Promise which would be used to defer the sequential-run. Thats very important and differs from an Event!

Methods

• registerHook(case, config)
• runHooks(case, input, [context])

registerHook(case, config)

• case - Name of the case given as a string.
• config
  • priority - Number to define execution order point (Default: 1000)
  • name - Name of the hook. Will be used as key on result-object.
  • handler(input, results) - Hook-handler which will be executed on run. Will have context as this if context is given in runHooks-method.

runHooks(case, input, [context])

• case - Name of the case which should be executed.
• input - Any type which should be injected into hook-handlers as input value.
• context - Optional execution context for handlers.

Example

atween.registerHook('test', {
    name: 'A',
    handler: (i) => i
});
 
// Will not have any effect on result-object cause missing name attribute.
atween.registerHook('test', (i) => console.log(i));
 
atween.registerHook('test', {
    name: 'B',
    handler: (i) => Promise.resolve(i * 2)
});
 
atween.registerHook('test', {
    name: 'C',
    priority: 500,
    handler: (i) => i * 3
});
 
atween.runHooks('test', 2)
    .then((res) => expect(res).to.equal({
        C: 6, // First assignment caused by priority of 500
        A: 2,
        B: 4
    }));

Events

Events work by the concept of "Fire and Forget". They will not wait for async operations of previous event-handlers. Its return value can be true or false but for logging purpose only.

Methods

• registerEvent(case, config)
• runEvents(case, input, [context])

registerEvent(case, config)

• case - Name of the case given as a string.
• config
  • priority - Number to define execution order point (Default: 1000)
  • name - Name of the hook. Will be used as key on result-object.
  • handler(input, results) - Hook-handler which will be executed on run. Will have context as this if context is given in runHooks-method.

runEvents(case, input, [context])

• case - Name of the case which should be executed.
• input - Any type which should be injected into event-handlers as input value.
• context - Optional execution context for handlers.