feat(common): add a titlecase pipe (#13324)

closes #11436

modules/@angular/common/src/pipes/case_conversion_pipes.ts

@@ -0,0 +1,61 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {Pipe, PipeTransform} from '@angular/core';
+import {InvalidPipeArgumentError} from './invalid_pipe_argument_error';
+
+/**
+ * Transforms text to lowercase.
+ *
+ * {@example  core/pipes/ts/lowerupper_pipe/lowerupper_pipe_example.ts region='LowerUpperPipe' }
+ *
+ * @stable
+ */
+@Pipe({name: 'lowercase'})
+export class LowerCasePipe implements PipeTransform {
+  transform(value: string): string {
+    if (!value) return value;
+    if (typeof value !== 'string') {
+      throw new InvalidPipeArgumentError(LowerCasePipe, value);
+    }
+    return value.toLowerCase();
+  }
+}
+
+/**
+ * Transforms text to titlecase.
+ *
+ * @stable
+ */
+@Pipe({name: 'titlecase'})
+export class TitleCasePipe implements PipeTransform {
+  transform(value: string): string {
+    if (!value) return value;
+    if (typeof value !== 'string') {
+      throw new InvalidPipeArgumentError(TitleCasePipe, value);
+    }
+
+    return value[0].toUpperCase() + value.substr(1).toLowerCase();
+  }
+}
+
+/**
+ * Transforms text to uppercase.
+ *
+ * @stable
+ */
+@Pipe({name: 'uppercase'})
+export class UpperCasePipe implements PipeTransform {
+  transform(value: string): string {
+    if (!value) return value;
+    if (typeof value !== 'string') {
+      throw new InvalidPipeArgumentError(UpperCasePipe, value);
+    }
+    return value.toUpperCase();
+  }
+}