feat(component): add support for invisible reCAPTCHA

fixes #18

README.md

@@ -187,3 +187,45 @@ add the `required` attribute to the `<recaptcha>` element
   formModel = new MyFormModel();
 }
 ```
+
+## <a name="example-invisible"></a>Working with invisible reCAPTCHA [(see in action)](https://dethariel.github.io/ng2-recaptcha/invisible)
+
+Working with [invisible reCAPTCHA](https://developers.google.com/recaptcha/docs/invisible) is almost the same as with regular one.
+First, you need to provide the right size:
+
+```html
+<recaptcha size="invisible" ...></recaptcha>
+```
+
+You will also need to invoke the [`"execute()"`](https://developers.google.com/recaptcha/docs/invisible#programmatic_execute) method manually. This can be done by either obtaining a reference to `RecaptchaComponent` via `@ViewChild()`, or by using inline template reference:
+
+```html
+<recaptcha #captchaRef="reCaptcha" ...></recaptcha>
+...
+<button (click)="captchaRef.execute()">Submit</button>
+```
+
+Normally you would only submit a form when recaptcha response has been received. This can be achieved by reacting to `(resolved)` event and invoking submit logic when the captcha response is truthy (this will not try to submit the form when recaptcha response has expired). A sample implementation would look like this:
+
+```typescript
+@Component({
+  selector: 'my-form',
+  template: `
+  <form>
+    <recaptcha
+      #captchaRef="reCaptcha"
+      siteKey="YOUR_SITE_KEY"
+      size="invisible"
+      (resolved)="$event && submit($event)"
+    ></recaptcha>
+    <button (click)="captchaRef.execute()">Submit</button>
+  </form>`,
+}) export class MyForm {
+  public submit(captchaResponse: string): void {
+    this.http.post({
+      captcha: captchaResponse,
+      /* ... */
+    });
+  }
+}
+```

recaptcha/recaptcha.component.ts

@@ -27,7 +27,7 @@ export class RecaptchaComponent implements AfterViewInit, OnDestroy {
   @Input() public siteKey: string;
   @Input() public theme: ReCaptchaV2.Theme;
   @Input() public type: ReCaptchaV2.Type;
-  @Input() public size: ReCaptchaV2.Size;
+  @Input() public size: ReCaptchaV2.Size | 'invisible';
   @Input() public tabIndex: number;
 
   @Output() public resolved = new EventEmitter<string>();
@@ -63,6 +63,21 @@ export class RecaptchaComponent implements AfterViewInit, OnDestroy {
     this.subscription.unsubscribe();
   }
 
+  /**
+   * Executes the invisible recaptcha.
+   * Does nothing if component's size is not set to "invisible".
+   */
+  public execute(): void {
+    if (this.size !== 'invisible') {
+      return;
+    }
+
+    if (this.widget != null) {
+      // tslint:disable-next-line:no-any
+      (this.grecaptcha as any).execute(this.widget);
+    }
+  }
+
   public reset() {
     if (this.widget != null) {
       if (this.grecaptcha.getResponse(this.widget)) {
@@ -96,7 +111,8 @@ export class RecaptchaComponent implements AfterViewInit, OnDestroy {
         this.zone.run(() => this.expired());
       },
       sitekey: this.siteKey,
-      size: this.size,
+      // tslint:disable-next-line:no-any
+      size: this.size as any,
       tabindex: this.tabIndex,
       theme: this.theme,
       type: this.type,