hooks

Add pre and post middleware hooks to your JavaScript methods.

Installation

npm install hooks

Motivation

Suppose you have a JavaScript object with a save method.

It would be nice to be able to declare code that runs before save and after save. For example, you might want to run validation code before every save, and you might want to dispatch a job to a background job queue after save.

One might have an urge to hard code this all into save, but that turns out to couple all these pieces of functionality (validation, save, and job creation) more tightly than is necessary. For example, what if someone does not want to do background job creation after the logical save.

It is nicer to tack on functionality using what we call pre and post hooks. These are functions that you define and that you direct to execute before or after particular methods.

Example

We can use hooks to add validation and background jobs in the following way: var hooks = require('hooks') , Model = require('./path/to/some/model/with/save');

// Add hooks' methods: `hook`, `pre`, and `post`    
for (var k in hooks) {
  Model.prototype[k] = hooks[k];
}

Model.hook('save', Model.prototype.save);

Model.pre('save', function validate (next, halt) {
  if (this.isValid()) next();
  else halt();
});

Model.post('save', function createJob (next, halt) {
  this.sendToBackgroundQueue();
});

Pres and Posts as Middleware

We structure pres and posts as middleware to give you maximum flexibility:

1. You can define multiple pres (or posts) for a single method.
2. These pres (or posts) are then executed as a chain of methods.
3. Any functions in this middleware chain can choose to halt the chain's execution. If this occurs, then none of the other middleware in the chain will execute, and the main method (e.g., save) will not execute. This is nice, for example, when we don't want a document to save if it is invalid.

Tests

To run the tests: make test

Contributors

• Brian Noguchi

License

MIT License

Author

Brian Noguchi