Update String#trim spec compliance

Check for two commonly erroneously trimmed characters instead of one, and check for erroneously failing to trim the trimmable whitespace characters. I would also replace `if (typeof this === 'undefined' || this === null)` with `if (this == null)` but I don't know whether that's allowed by this library's style rules.
paulmillr · Aug 23, 2015 · f337db9 · f337db9
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diff --git a/es6-shim.js b/es6-shim.js
@@ -644,16 +644,17 @@
     overrideNative(String.prototype, 'includes', StringPrototypeShims.includes);
   }
 
-  var hasStringTrimBug = '\u0085'.trim().length !== 1;
+  // whitespace from: http://es5.github.io/#x15.5.4.20
+  // implementation from https://github.com/es-shims/es5-shim/blob/v3.4.0/es5-shim.js#L1304-L1324
+  var wsp = '\t\n\v\f\r \xA0\u1680\u180E\u2000\u2001\u2002\u2003\u2004\u2005' +
+    '\u2006\u2007\u2008\u2009\u200A\u2028\u2029\u202F\u205F\u3000\uFEFF';
+  var nxtLine = '\x85';
+  var zeroWidth = '\u200B';
+  var hasStringTrimBug = wsp.trim() || !nxtLine.trim() || !zeroWidth.trim();
   if (hasStringTrimBug) {
     delete String.prototype.trim;
-    // whitespace from: http://es5.github.io/#x15.5.4.20
-    // implementation from https://github.com/es-shims/es5-shim/blob/v3.4.0/es5-shim.js#L1304-L1324
-    var ws = [
-      '\x09\x0A\x0B\x0C\x0D\x20\xA0\u1680\u180E\u2000\u2001\u2002\u2003',
-      '\u2004\u2005\u2006\u2007\u2008\u2009\u200A\u202F\u205F\u3000\u2028',
-      '\u2029\uFEFF'
-    ].join('');
+    var ws = '\t-\r \xA0\u1680\u180E\u2000-\u200A\u2028\u2029\u202F\u205F' +
+      '\u3000\uFEFF';
     var trimRegexp = new RegExp('(^[' + ws + ']+)|([' + ws + ']+$)', 'g');
     defineProperties(String.prototype, {
       trim: function trim() {

diff --git a/test/string.js b/test/string.js
@@ -587,13 +587,14 @@ var runStringTests = function () {
       });
 
       it('should trim the correct characters', function () {
-        var whitespace = '\u0009' + '\u000b' + '\u000c' + '\u0020' +
-                         '\u00a0' + '\u1680' + '\u2000' + '\u2001' +
-                         '\u2002' + '\u2003' + '\u2004' + '\u2005' +
-                         '\u2006' + '\u2007' + '\u2008' + '\u2009' +
-                         '\u200A' + '\u202f' + '\u205f' + '\u3000';
+        var whitespace = '\u0009' + '\u000B' + '\u000C' + '\u0020' +
+                         '\u00A0' + '\u1680' + '\u180E' + '\u2000' +
+                         '\u2001' + '\u2002' + '\u2003' + '\u2004' +
+                         '\u2005' + '\u2006' + '\u2007' + '\u2008' +
+                         '\u2009' + '\u200A' + '\u202F' + '\u205F' +
+                         '\u3000' + '\uFEFF';
 
-        var lineTerminators = '\u000a' + '\u000d' + '\u2028' + '\u2029';
+        var lineTerminators = '\u000A' + '\u000D' + '\u2028' + '\u2029';
 
         var trimmed = (whitespace + lineTerminators).trim();
         expect(trimmed).to.have.property('length', 0);
@@ -606,6 +607,12 @@ var runStringTests = function () {
         expect(trimmed).to.equal('\u0085');
       });
 
+      it('should not trim U+200B', function () {
+        var trimmed = '\u200B'.trim();
+        expect(trimmed).to.have.property('length', 1);
+        expect(trimmed).to.equal('\u200B');
+      });
+
       it('should trim on both sides', function () {
         var trimmed = ' a '.trim();
         expect(trimmed).to.have.property('length', 1);