feat: add filter() function

index.js

@@ -320,6 +320,40 @@ Kareem.prototype.wrap = function(name, fn, context, args, options) {
   });
 };
 
+Kareem.prototype.filter = function(fn) {
+  const clone = this.clone();
+
+  const pres = Array.from(clone._pres.keys());
+  for (const name of pres) {
+    const hooks = this._pres.get(name).
+      map(h => Object.assign({}, h, { name: name })).
+      filter(fn);
+
+    if (hooks.length === 0) {
+      clone._pres.delete(name);
+      continue;
+    }
+
+    clone._pres.set(name, hooks);
+  }
+
+  const posts = Array.from(clone._posts.keys());
+  for (const name of posts) {
+    const hooks = this._posts.get(name).
+      map(h => Object.assign({}, h, { name: name })).
+      filter(fn);
+
+    if (hooks.length === 0) {
+      clone._posts.delete(name);
+      continue;
+    }
+
+    clone._posts.set(name, hooks);
+  }
+
+  return clone;
+};
+
 Kareem.prototype.hasHooks = function(name) {
   return this._pres.has(name) || this._posts.has(name);
 };

test/misc.test.js

@@ -31,3 +31,41 @@ describe('merge', function() {
     assert.equal(k3._pres.get('cook').numAsync, 1);
   });
 });
+
+describe('filter', function() {
+  it('returns clone with only hooks that match `fn()`', function() {
+    const k1 = new Kareem();
+
+    k1.pre('update', { document: true }, f1);
+    k1.pre('update', { query: true }, f2);
+    k1.pre('remove', { document: true }, f3);
+
+    k1.post('update', { document: true }, f1);
+    k1.post('update', { query: true }, f2);
+    k1.post('remove', { document: true }, f3);
+
+    const k2 = k1.filter(hook => hook.document);
+    assert.equal(k2._pres.get('update').length, 1);
+    assert.equal(k2._pres.get('update')[0].fn, f1);
+    assert.equal(k2._pres.get('remove').length, 1);
+    assert.equal(k2._pres.get('remove')[0].fn, f3);
+
+    assert.equal(k2._posts.get('update').length, 1);
+    assert.equal(k2._posts.get('update')[0].fn, f1);
+    assert.equal(k2._posts.get('remove').length, 1);
+    assert.equal(k2._posts.get('remove')[0].fn, f3);
+
+    const k3 = k1.filter(hook => hook.query);
+    assert.equal(k3._pres.get('update').length, 1);
+    assert.equal(k3._pres.get('update')[0].fn, f2);
+    assert.ok(!k3._pres.has('remove'));
+
+    assert.equal(k3._posts.get('update').length, 1);
+    assert.equal(k3._posts.get('update')[0].fn, f2);
+    assert.ok(!k3._posts.has('remove'));
+
+    function f1() {}
+    function f2() {}
+    function f3() {}
+  });
+});