mongoosejs / kareem

Next-generation take on pre/post function hooks

kareem

Re-imagined take on the hooks module, meant to offer additional flexibility in allowing you to execute hooks whenever necessary, as opposed to simply wrapping a single function.

Named for the NBA's all-time leading scorer Kareem Abdul-Jabbar, known for his mastery of the hook shot

API

pre hooks

Much like hooks, kareem lets you define pre and post hooks: pre hooks are called before a given function executes. Unlike hooks, kareem stores hooks and other internal state in a separate object, rather than relying on inheritance. Furthermore, kareem exposes an execPre() function that allows you to execute your pre hooks when appropriate, giving you more fine-grained control over your function hooks.

It runs without any hooks specified

hooks.execPre('cook', null, function() {
  // ...
});

It runs basic serial pre hooks

pre hook functions take one parameter, a "done" function that you execute when your pre hook is finished.

var count = 0;

hooks.pre('cook', function(done) {
  ++count;
  done();
});

hooks.execPre('cook', null, function() {
  assert.equal(1, count);
});

It can run multipe pre hooks

var count1 = 0;
var count2 = 0;

hooks.pre('cook', function(done) {
  ++count1;
  done();
});

hooks.pre('cook', function(done) {
  ++count2;
  done();
});

hooks.execPre('cook', null, function() {
  assert.equal(1, count1);
  assert.equal(1, count2);
});

It can run fully synchronous pre hooks

If your pre hook function takes no parameters, its assumed to be fully synchronous.

var count1 = 0;
var count2 = 0;

hooks.pre('cook', function() {
  ++count1;
});

hooks.pre('cook', function() {
  ++count2;
});

hooks.execPre('cook', null, function(error) {
  assert.equal(null, error);
  assert.equal(1, count1);
  assert.equal(1, count2);
});

It properly attaches context to pre hooks

Pre save hook functions are bound to the second parameter to execPre()

hooks.pre('cook', function(done) {
  this.bacon = 3;
  done();
});

hooks.pre('cook', function(done) {
  this.eggs = 4;
  done();
});

var obj = { bacon: 0, eggs: 0 };

// In the pre hooks, `this` will refer to `obj`
hooks.execPre('cook', obj, function(error) {
  assert.equal(null, error);
  assert.equal(3, obj.bacon);
  assert.equal(4, obj.eggs);
});

It can execute parallel (async) pre hooks

Like the hooks module, you can declare "async" pre hooks - these take two parameters, the functions next() and done(). next() passes control to the next pre hook, but the underlying function won't be called until all async pre hooks have called done().

hooks.pre('cook', true, function(next, done) {
  this.bacon = 3;
  next();
  setTimeout(function() {
    done();
  }, 5);
});

hooks.pre('cook', true, function(next, done) {
  next();
  var _this = this;
  setTimeout(function() {
    _this.eggs = 4;
    done();
  }, 10);
});

hooks.pre('cook', function(next) {
  this.waffles = false;
  next();
});

var obj = { bacon: 0, eggs: 0 };

hooks.execPre('cook', obj, function() {
  assert.equal(3, obj.bacon);
  assert.equal(4, obj.eggs);
  assert.equal(false, obj.waffles);
});

It supports returning a promise

You can also return a promise from your pre hooks instead of calling next(). When the returned promise resolves, kareem will kick off the next middleware.

hooks.pre('cook', function() {
  return new Promise(resolve => {
    setTimeout(() => {
      this.bacon = 3;
      resolve();
    }, 100);
  });
});

var obj = { bacon: 0 };

hooks.execPre('cook', obj, function() {
  assert.equal(3, obj.bacon);
});

post hooks

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It runs without any hooks specified

hooks.execPost('cook', null, [1], function(error, eggs) {
  assert.ifError(error);
  assert.equal(1, eggs);
  done();
});

It executes with parameters passed in

hooks.post('cook', function(eggs, bacon, callback) {
  assert.equal(1, eggs);
  assert.equal(2, bacon);
  callback();
});

hooks.execPost('cook', null, [1, 2], function(error, eggs, bacon) {
  assert.ifError(error);
  assert.equal(1, eggs);
  assert.equal(2, bacon);
});

It can use synchronous post hooks

var execed = {};

hooks.post('cook', function(eggs, bacon) {
  execed.first = true;
  assert.equal(1, eggs);
  assert.equal(2, bacon);
});

hooks.post('cook', function(eggs, bacon, callback) {
  execed.second = true;
  assert.equal(1, eggs);
  assert.equal(2, bacon);
  callback();
});

hooks.execPost('cook', null, [1, 2], function(error, eggs, bacon) {
  assert.ifError(error);
  assert.equal(2, Object.keys(execed).length);
  assert.ok(execed.first);
  assert.ok(execed.second);
  assert.equal(1, eggs);
  assert.equal(2, bacon);
});

It supports returning a promise

You can also return a promise from your post hooks instead of calling next(). When the returned promise resolves, kareem will kick off the next middleware.

hooks.post('cook', function(bacon) {
  return new Promise(resolve => {
    setTimeout(() => {
      this.bacon = 3;
      resolve();
    }, 100);
  });
});

var obj = { bacon: 0 };

hooks.execPost('cook', obj, obj, function() {
  assert.equal(obj.bacon, 3);
});

wrap()

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It wraps pre and post calls into one call

hooks.pre('cook', true, function(next, done) {
  this.bacon = 3;
  next();
  setTimeout(function() {
    done();
  }, 5);
});

hooks.pre('cook', true, function(next, done) {
  next();
  var _this = this;
  setTimeout(function() {
    _this.eggs = 4;
    done();
  }, 10);
});

hooks.pre('cook', function(next) {
  this.waffles = false;
  next();
});

hooks.post('cook', function(obj) {
  obj.tofu = 'no';
});

var obj = { bacon: 0, eggs: 0 };

var args = [obj];
args.push(function(error, result) {
  assert.ifError(error);
  assert.equal(null, error);
  assert.equal(3, obj.bacon);
  assert.equal(4, obj.eggs);
  assert.equal(false, obj.waffles);
  assert.equal('no', obj.tofu);

  assert.equal(obj, result);
});

hooks.wrap(
  'cook',
  function(o, callback) {
    assert.equal(3, obj.bacon);
    assert.equal(4, obj.eggs);
    assert.equal(false, obj.waffles);
    assert.equal(undefined, obj.tofu);
    callback(null, o);
  },
  obj,
  args);

createWrapper()

It wraps wrap() into a callable function

hooks.pre('cook', true, function(next, done) {
  this.bacon = 3;
  next();
  setTimeout(function() {
    done();
  }, 5);
});

hooks.pre('cook', true, function(next, done) {
  next();
  var _this = this;
  setTimeout(function() {
    _this.eggs = 4;
    done();
  }, 10);
});

hooks.pre('cook', function(next) {
  this.waffles = false;
  next();
});

hooks.post('cook', function(obj) {
  obj.tofu = 'no';
});

var obj = { bacon: 0, eggs: 0 };

var cook = hooks.createWrapper(
  'cook',
  function(o, callback) {
    assert.equal(3, obj.bacon);
    assert.equal(4, obj.eggs);
    assert.equal(false, obj.waffles);
    assert.equal(undefined, obj.tofu);
    callback(null, o);
  },
  obj);

cook(obj, function(error, result) {
  assert.ifError(error);
  assert.equal(3, obj.bacon);
  assert.equal(4, obj.eggs);
  assert.equal(false, obj.waffles);
  assert.equal('no', obj.tofu);

  assert.equal(obj, result);
});

clone()

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It clones a Kareem object

var k1 = new Kareem();
k1.pre('cook', function() {});
k1.post('cook', function() {});

var k2 = k1.clone();
assert.deepEqual(Array.from(k2._pres.keys()), ['cook']);
assert.deepEqual(Array.from(k2._posts.keys()), ['cook']);

merge()

It pulls hooks from another Kareem object

var k1 = new Kareem();
var test1 = function() {};
k1.pre('cook', test1);
k1.post('cook', function() {});

var k2 = new Kareem();
var test2 = function() {};
k2.pre('cook', test2);
var k3 = k2.merge(k1);
assert.equal(k3._pres.get('cook').length, 2);
assert.equal(k3._pres.get('cook')[0].fn, test2);
assert.equal(k3._pres.get('cook')[1].fn, test1);
assert.equal(k3._posts.get('cook').length, 1);