Add polyfills for String.prototype.trim{Left,Right}()

Most browsers have had these methods since the ES5 era,
but they were never officially part of the language until ES_2019,
so some (e.g. IE11) don't.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=255615448

src/com/google/javascript/jscomp/js/es6/string/trimend.js

@@ -20,6 +20,21 @@
  */
 'require util/polyfill';
 
+// Most browsers implemented trimRight around ES5-time-frame, but it wasn't
+// officially part of the language specification until ES_2019, so we have
+// to provide a polyfill for it.
+// IE11 doesn't have it, of course...
+$jscomp.polyfill('String.prototype.trimRight', function(orig) {
+  /**
+   * @this {string}
+   * @return {string}
+   */
+  function polyfill() {
+    return this.replace(/[\s\xa0]+$/, '');
+  }
+  return orig || polyfill;
+}, 'es_2019', 'es3');
+
 $jscomp.polyfill('String.prototype.trimEnd', function(orig) {
   return orig || String.prototype.trimRight;
 }, 'es_2019', 'es3');

src/com/google/javascript/jscomp/js/es6/string/trimstart.js

@@ -20,6 +20,21 @@
  */
 'require util/polyfill';
 
+// Most browsers implemented trimLeft around ES5-time-frame, but it wasn't
+// officially part of the language specification until ES_2019, so we have
+// to provide a polyfill for it.
+// IE11 doesn't have it, of course...
+$jscomp.polyfill('String.prototype.trimLeft', function(orig) {
+  /**
+   * @this {string}
+   * @return {string}
+   */
+  function polyfill() {
+    return this.replace(/^[\s\xa0]+/, '');
+  }
+  return orig || polyfill;
+}, 'es_2019', 'es3');
+
 $jscomp.polyfill('String.prototype.trimStart', function(orig) {
   return orig || String.prototype.trimLeft;
 }, 'es_2019', 'es3');

src/com/google/javascript/jscomp/js/polyfills.txt

@@ -72,6 +72,8 @@ String.prototype.padStart es8 es3 es6/string/padstart
 String.prototype.repeat es6 es3 es6/string/repeat
 String.prototype.startsWith es6 es3 es6/string/startswith
 String.prototype.trimEnd es_2019 es3 es6/string/trimend
+String.prototype.trimLeft es_2019 es3 es6/string/trimstart
+String.prototype.trimRight es_2019 es3 es6/string/trimend
 String.prototype.trimStart es_2019 es3 es6/string/trimstart
 String.raw es6 es6
 WeakMap es6 es3 es6/weakmap

test/com/google/javascript/jscomp/runtime_tests/polyfill_tests/string_trim_end.js → test/com/google/javascript/jscomp/runtime_tests/polyfill_tests/string_trim_end_test.js

@@ -22,15 +22,23 @@ const testSuite = goog.require('goog.testing.testSuite');
 testSuite({
   testTrimEnd_noChange() {
     assertEquals('a', 'a'.trimEnd());
+    assertEquals('a', 'a'.trimRight());
     assertEquals('ab', 'ab'.trimEnd());
+    assertEquals('ab', 'ab'.trimRight());
     assertEquals('a b', 'a b'.trimEnd());
+    assertEquals('a b', 'a b'.trimRight());
     assertEquals(' <-', ' <-'.trimEnd());
+    assertEquals(' <-', ' <-'.trimRight());
     assertEquals('\t<-', '\t<-'.trimEnd());
+    assertEquals('\t<-', '\t<-'.trimRight());
   },
 
   testTrimEnd_change() {
-    assertTrue('->', '-> '.trimEnd());
-    assertTrue('->', '->         '.trimEnd());
-    assertTrue('->', '->\t'.trimEnd());
+    assertEquals('->', '-> '.trimEnd());
+    assertEquals('->', '-> '.trimRight());
+    assertEquals('->', '->         '.trimEnd());
+    assertEquals('->', '->         '.trimRight());
+    assertEquals('->', '->\t'.trimEnd());
+    assertEquals('->', '->\t'.trimRight());
   },
 });

test/com/google/javascript/jscomp/runtime_tests/polyfill_tests/string_trim_start.js → test/com/google/javascript/jscomp/runtime_tests/polyfill_tests/string_trim_start_test.js

@@ -22,15 +22,23 @@ const testSuite = goog.require('goog.testing.testSuite');
 testSuite({
   testTrimStart_noChange() {
     assertEquals('a', 'a'.trimStart());
+    assertEquals('a', 'a'.trimLeft());
     assertEquals('ab', 'ab'.trimStart());
+    assertEquals('ab', 'ab'.trimLeft());
     assertEquals('a b', 'a b'.trimStart());
+    assertEquals('a b', 'a b'.trimLeft());
     assertEquals('-> ', '-> '.trimStart());
+    assertEquals('-> ', '-> '.trimLeft());
     assertEquals('->\t', '->\t'.trimStart());
+    assertEquals('->\t', '->\t'.trimLeft());
   },
 
   testTrimStart_change() {
     assertEquals('<-', ' <-'.trimStart());
+    assertEquals('<-', ' <-'.trimLeft());
     assertEquals('<-', '\t<-'.trimStart());
+    assertEquals('<-', '\t<-'.trimLeft());
     assertEquals('<-', '         <-'.trimStart());
+    assertEquals('<-', '         <-'.trimLeft());
   },
 });