Fix possible regex dos vulnerability.

Reported via: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-7753
Adapted solution from: http://blog.stevenlevithan.com/archives/faster-trim-javascript

index.js

@@ -1,17 +1,22 @@
-
 exports = module.exports = trim;
 
 function trim(str){
   if (str.trim) return str.trim();
-  return str.replace(/^\s*|\s*$/g, '');
+  return exports.right(exports.left(str));
 }
 
 exports.left = function(str){
   if (str.trimLeft) return str.trimLeft();
-  return str.replace(/^\s*/, '');
+
+  return str.replace(/^\s\s*/, '');
 };
 
 exports.right = function(str){
   if (str.trimRight) return str.trimRight();
-  return str.replace(/\s*$/, '');
+
+  var whitespace_pattern = /\s/,
+      i = str.length;
+  while (whitespace_pattern.test(str.charAt(--i)));
+
+  return str.slice(0, i + 1);
 };

test/trim.js

@@ -7,6 +7,14 @@ describe('trim(str)', function(){
     trim('  foo bar  ').should.equal('foo bar');
     trim('\n\n\nfoo bar\n\r\n\n').should.equal('foo bar');
   })
+
+  it('should supply implementation of trim() if needed', function() {
+    var str1 = new String('  foo bar  ');
+    str1.trim = null;
+    str1.trimLeft = null;
+    str1.trimRight = null;
+    trim(str1).should.equal('foo bar');
+  })
 })
 
 describe('.left(str)', function(){