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() {
      done();
    });

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);
      done();
    });

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);
      done();
    });

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);
      done();
    });

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);
      done();
    });

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);
      done();
    });

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);
      done();
    });

post hooks

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);
      done();
    });

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);
      done();
    });

wrap()

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);
      done();
    });

    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);
      done();
    });

clone()

It clones a Kareem object

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

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

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['cook'].length, 2);
    assert.equal(k3._pres['cook'][0].fn, test2);
    assert.equal(k3._pres['cook'][1].fn, test1);
    assert.equal(k3._posts['cook'].length, 1);

Works with Promise/async function

Wrap an async function:

  var calledPre = 0;
  var calledFn = 0;
  var calledPost = 0;
  hooks.pre('cook', async(done)=>++calledPre && done());
  hooks.post('cook', async(callback)=>++calledPost);
  var wrapper = hooks.createWrapper('cook', async function(){ ++calledFn});
  await wrapper();
  assert.equal(calledPre, 1);
  assert.equal(calledFn, 1);
  assert.equal(calledPost, 1);

Wrap a function which returns a promise

Set options.asyncFunc = true;

Set options.forceWrap = ture, to fore wrap the function for bonding the pre/post hooks later.

    var calledPre = 0;
    var calledFn = 0;
    var calledPost = 0;
    var wrapper = hooks.createWrapper('cook',
      function(a,b){return new Promise((resolve, rejece)=>{
        ++calledFn;
        b.a++;
        resolve([++a, b]);
      })},
      null,
      {
        forceWrap:true,  // wrap the function before setting hooks.
        asyncFunc:true   //tell the wrapper the function will return a promise.
      }
    );
    hooks.pre('cook', async(done)=>++calledPre && done());
    hooks.post('cook', async(result)=>{
      ++calledPost;
      assert.equal(result[0], 2);
      assert.equal(result[1].a, 3);
    });
    await wrapper(1,{a:2});
    assert.equal(calledPre, 1);
    assert.equal(calledFn, 1);
    assert.equal(calledPost, 1);

ShortCut by pre-hooks

Sometime the pre-hook got the result(by cache), and need to terminate the wrapped function and return the result.

send the result to done() function

    var calledPre = 0;
    var calledFn = 0;
    var calledPost = 0;
    hooks.pre('cook', async(done, id)=>{
      assert.equal(1, id);
      calledPre++;
      done(null, 2);  //short-cut and return 2;
    });
    hooks.post('cook', async(result)=>{
      assert.ok(false);
      calledPost++;
    });
    var wrapper = hooks.createWrapper('cook', async function(id){
      calledFn++;
      return ++id;
    });
    var result = await wrapper(1);
    assert.equal(result, 2); //got the right result by pre-hooks.
    assert.equal(calledPre, 1);
    assert.equal(calledFn, 0); //the wrapped function never run.
    assert.equal(calledPost, 0);
  })