feat(signal): enable signaling one-time bindings

fixes #176

src/signal-binding-behavior.js

@@ -13,9 +13,6 @@ export class SignalBindingBehavior {
     if (!binding.updateTarget) {
       throw new Error('Only property bindings and string interpolation bindings can be signaled.  Trigger, delegate and call bindings cannot be signaled.');
     }
-    if (binding.mode === bindingMode.oneTime) {
-      throw new Error('One-time bindings cannot be signaled.');
-    }
     let bindings = this.signals[name] || (this.signals[name] = []);
     bindings.push(binding);
     binding.signalName = name;

test/signal-binding-behavior.spec.js

@@ -29,13 +29,13 @@ describe('SignalBindingBehavior', () => {
     bindingSignaler = container.get(BindingSignaler);
   });
 
-  it('should throw in one-time binding', () => {
+  it('should not throw in one-time binding', () => {
     let source = {};
     let scope = createScopeForTest(source);
     let target = document.createElement('input');
     let bindingExpression = bindingEngine.createBindingExpression('value', `'foo' & signal:'test'`, bindingMode.oneTime, lookupFunctions);
     let binding = bindingExpression.createBinding(target);
-    expect(() => binding.bind(scope)).toThrow();
+    expect(() => binding.bind(scope)).not.toThrow();
   });
 
   it('should signal binding', () => {
@@ -52,6 +52,20 @@ describe('SignalBindingBehavior', () => {
     expect(target.value).toBe(converterResult);
   });
 
+  it('should signal one-time binding', () => {
+    let source = { updateDateTime: new Date() };
+    let scope = createScopeForTest(source);
+    let target = document.createElement('input');
+    let bindingExpression = bindingEngine.createBindingExpression('value', `updateDateTime | testConverter & signal:'test'`, bindingMode.oneTime, lookupFunctions);
+    let binding = bindingExpression.createBinding(target);
+    converterResult = 'hello';
+    binding.bind(scope);
+    expect(target.value).toBe(converterResult);
+    converterResult = 'world';
+    bindingSignaler.signal('test');
+    expect(target.value).toBe(converterResult);
+  });
+
   it('should signal interpolation binding', () => {
     let source = { updateDateTime: new Date() };
     let scope = createScopeForTest(source);