step-cascade v3.1.4

StepCascade

This is a small collection of classes which can be used to build a chain of "steps" all manipulating a common payload object.

Table of Contents

• Usage
  • Error Handling
    • Recoverable Errors by Step
    • Recoverable Errors by Cascade
    • Recoverable Callbacks
• Testing
• Contribution

Usage

Let's say we have a payload like this:

type User = {
  firstname: string;
  lastname: string;
};

Then we can write steps that are typed to this payload:

class FirstnameStep extends AbstractCascadingStep<User> {
  run(payload: StringArrayPayload): StringArrayPayload {
    payload.firstname = "Solaire";
    return payload;
  }
}

class LastnameStep extends AbstractCascadingStep<User> {
  run(payload: StringArrayPayload): StringArrayPayload {
    payload.lastname = "of Astora";
    return payload;
  }
}

We can then use the StepCascade to add those steps and have them manipulate the payload:

const cascade = new StepCascade<User>().addStep({ step: new FirstnameStep() }).addStep({ step: new LastnameStep() });

const result = await cascade.run({} as User);

console.log(result.firstname); // Solaire
console.log(result.lastname); // of Astora

Error Handling

The default error handling behaviour is quite simple. If one of your steps throws an error, the rest of the steps don't get executed.

const cascade = new StepCascade<User>().addStep({ step: new ErrorCausingStep() }).addStep({ step: new LastnameSTep() }); // Will never get called

The error being thrown by the StepCascade will be wrapped in a StepError, which will include the current StepDescription.

However, you can identify recoverable errors, ie. errors that can be resolved by different user input, for example. If a recoverable error gets identified, the step will try again.

There are two possibilities of identifying recoverable errors.

Recoverable Errors by Step

AbstractCascadingStep provides a function identifyRecoverableError. If an error gets thrown while executing this step, the function will be called. If it returns true, the step will be repeated.

Recoverable Errors by Cascade

Alternatively, you can call the function setIdentifyRecoverableErrorFunction on the StepCascade:

const recover: TIdentifyRecoverableError = (error: any) => {
  return (error.message = "A certain error message");
};
stepCascade.setIdentifyRecoverableErrorFunction(recover);

If the function returns true, the StepCascade will retry the current step, regardless of which step it is.

Recoverable Callbacks

If the error is recoverable, the StepCascade will call a callback function you can provide with the setRecoverableCallback function. This is typically used to ask the user if they want to try again.

stepCascade.setRecoverableCallback((error: any) => {
  console.log("An error occured, do you want to try again?");
  /* user input */
});

Testing

Simply run "npm test".

Contribution

Pull Requests are more than welcome!