createChainedFunction improvements

src/utils/createChainedFunction.js

@@ -4,22 +4,26 @@
  * Will only create a new function if needed,
  * otherwise will pass back existing functions or null.
  *
- * @param {function} one
- * @param {function} two
+ * @param {function} functions to chain
  * @returns {function|null}
  */
-function createChainedFunction(one, two) {
-  let hasOne = typeof one === 'function';
-  let hasTwo = typeof two === 'function';
+function createChainedFunction(...funcs) {
+  return funcs
+    .filter(f => f != null)
+    .reduce((acc, f) => {
+      if (typeof f !== 'function') {
+        throw new Error('Invalid Argument Type, must only provide functions, undefined, or null.');
+      }
 
-  if (!hasOne && !hasTwo) { return null; }
-  if (!hasOne) { return two; }
-  if (!hasTwo) { return one; }
+      if (acc === null) {
+        return f;
+      }
 
-  return function chainedFunction() {
-    one.apply(this, arguments);
-    two.apply(this, arguments);
-  };
+      return function chainedFunction(...args) {
+        acc.apply(this, args);
+        f.apply(this, args);
+      };
+    }, null);
 }
 
 export default createChainedFunction;

test/utils/createChainedFunctionSpec.js

@@ -0,0 +1,71 @@
+/* eslint no-new-func: 0 */
+import createChainedFunction from '../../src/utils/createChainedFunction';
+
+describe('createChainedFunction', function() {
+  it('returns null with no arguments', function() {
+    expect(createChainedFunction()).to.equal(null);
+  });
+
+  it('returns original function when single function is provided', function() {
+    const func1 = sinon.stub();
+    createChainedFunction(func1).should.equal(func1);
+  });
+
+  it('wraps two functions with another that invokes both when called', function() {
+    const func1 = sinon.stub();
+    const func2 = sinon.stub();
+    const chained = createChainedFunction(func1, func2);
+
+    chained
+      .should.not.equal(func1)
+      .and.should.not.equal(func2);
+
+    func1.should.not.have.been.called;
+    func2.should.not.have.been.called;
+
+    chained();
+
+    func1.should.have.been.calledOnce;
+    func2.should.have.been.calledOnce;
+  });
+
+  it('wraps multiple functions and invokes them in the order provided', function() {
+    const results = [];
+    const func1 = () => results.push(1);
+    const func2 = () => results.push(2);
+    const func3 = () => results.push(3);
+    const chained = createChainedFunction(func1, func2, func3);
+    chained();
+    results.should.eql([1, 2, 3]);
+  });
+
+  it('forwards arguments to all chained functions', function() {
+    const in1 = 'herpa derpa';
+    const in2 = {
+      herpa: 'derpa'
+    };
+
+    const func = (arg1, arg2) => {
+      arg1.should.equal(in1);
+      arg2.should.equal(in2);
+    };
+
+    const chained = createChainedFunction(func, func, func);
+    chained(in1, in2);
+  });
+
+  it('throws when func is not provided', function() {
+    expect(() => {
+      createChainedFunction({ herpa: 'derpa' });
+    }).to.throw(/Invalid Argument Type/);
+  });
+
+  it('works with new Function call', function() {
+    const results = [];
+    const func1 = new Function('results', 'results.push(1);');
+    const func2 = new Function('results', 'results.push(2);');
+    const chained = createChainedFunction(func1, func2);
+    chained(results);
+    results.should.eql([1, 2]);
+  });
+});