add stripLeft and stripRight method

README.md

@@ -702,6 +702,27 @@ S(' 1 2 3--__--4 5 6-7__8__9--0').strip(' ', '_', '-').s; //'1234567890'
 S('can words also be stripped out?').strip('words', 'also', 'be').s; //'can    stripped out?'
 ```
 
+### - stripLeft([chars]) ###
+Returns a new string in which all chars have been stripped from the beginning of the string (default whitespace characters).
+
+Example:
+
+```javascript
+S('  hello ').stripLeft().s; //'hello '
+S('abcz').stripLeft('a-z').s; //'bcz'
+S('www.example.com').stripLeft('w.').s; //'example.com'
+```
+
+### - stripRight([chars]) ###
+Returns a new string in which all chars have been stripped from the end of the string (default whitespace characters).
+
+Example:
+
+```javascript
+S('  hello ').stripRight().s; //'  hello'
+S('abcz').stripRight('a-z').s; //'abc'
+```
+
 
 ### - stripPunctuation()
 

lib/string.js

@@ -355,6 +355,38 @@ string.js - Copyright (C) 2012-2014, JP Richardson <jprichardson@gmail.com>
       return new this.constructor(ss);
     },
 
+    stripLeft: function (chars) {
+      var regex;
+      var pattern;
+      var ss = ensureString(this.s);
+
+      if (chars === undefined) {
+        pattern = /^\s+/g;
+      }
+      else {
+        regex = escapeRegExp(chars);
+        pattern = new RegExp("^[" + regex + "]+", "g");
+      }
+
+      return new this.constructor(ss.replace(pattern, ""));
+    },
+
+    stripRight: function (chars) {
+      var regex;
+      var pattern;
+      var ss = ensureString(this.s);
+
+      if (chars === undefined) {
+        pattern = /\s+$/g;
+      }
+      else {
+        regex = escapeRegExp(chars);
+        pattern = new RegExp("[" + regex + "]+$", "g");
+      }
+
+      return new this.constructor(ss.replace(pattern, ""));
+    },
+
     right: function(N) {
       if (N >= 0) {
         var s = this.s.substr(this.s.length - N, N);
@@ -757,6 +789,35 @@ string.js - Copyright (C) 2012-2014, JP Richardson <jprichardson@gmail.com>
     amp: '&'
   };
 
+  function escapeRegExp (s) {
+    // most part from https://github.com/skulpt/skulpt/blob/ecaf75e69c2e539eff124b2ab45df0b01eaf2295/src/str.js#L242
+    var c;
+    var i;
+    var ret = [];
+    var re = /^[A-Za-z0-9]+$/;
+    s = ensureString(s);
+    for (i = 0; i < s.length; ++i) {
+      c = s.charAt(i);
+
+      if (re.test(c)) {
+        ret.push(c);
+      }
+      else {
+        if (c === "\\000") {
+          ret.push("\\000");
+        }
+        else {
+          ret.push("\\" + c);
+        }
+      }
+    }
+    return ret.join("");
+  }
+
+  function ensureString(string) {
+    return string == null ? '' : '' + string;
+  }
+
   //from underscore.string
   var reversedEscapeChars = {};
   for(var key in escapeChars){ reversedEscapeChars[escapeChars[key]] = key; }

test/string.test.js

@@ -427,6 +427,55 @@
       })
     })
 
+    describe('- stripLeft(chars)', function () {
+
+      it('should return the new string with all occurences of `chars` removed from left', function () {
+        T (S('hello').stripLeft().s === 'hello');
+        T (S('hello').stripLeft('').s === 'hello');
+        T (S('  hello  ').stripLeft().s === 'hello  ');
+        T (S('foo ').stripLeft().s === 'foo ');
+        T (S('').stripLeft().s === '');
+        T (S(null).stripLeft().s === '');
+        T (S(undefined).stripLeft().s === '');
+        T (S('aazz').stripLeft('a').s === 'zz');
+        T (S('yytest').stripLeft('t').s === 'yytest');
+        T (S('xxxyyxx').stripLeft('x').s === 'yyxx');
+        T (S('abcz').stripLeft('a-z').s === 'bcz');
+        T (S('z alpha z').stripLeft('a-z').s === ' alpha z');
+        T (S('_-foobar-_').stripLeft('_-').s === 'foobar-_');
+
+        T (S('_.foo-_').stripLeft('_.').s === 'foo-_');
+        T (S('?foo ').stripLeft('?').s === 'foo ');
+        T (S('[$]hello-^').stripLeft('^[a-z]$').s === 'hello-^');
+
+        T (S(123).stripLeft(1).s === '23');
+      });
+    });
+
+    describe('- stripRight(chars)', function () {
+
+      it('should return the new string with all occurences of `chars` removed from right', function () {
+        T (S('hello').stripRight().s === 'hello');
+        T (S('hello').stripRight('').s === 'hello');
+        T (S('  hello  ').stripRight().s === '  hello');
+        T (S('  foo').stripRight().s === '  foo');
+        T (S('').stripRight().s === '');
+        T (S(null).stripRight().s === '');
+        T (S(undefined).stripRight().s === '');
+        T (S('aazz').stripRight('z').s === 'aa');
+        T (S('xxxyyxx').stripRight('x').s === 'xxxyy');
+        T (S('abcz').stripRight('a-z').s === 'abc');
+        T (S('z alpha z').stripRight('a-z').s === 'z alpha ');
+        T (S('_-foobar-_').stripRight('_-').s === '_-foobar');
+
+        T (S('_.foo_.').stripRight('_.').s === '_.foo');
+        T (S(' foo?').stripRight('?').s === ' foo');
+        T (S('[$]hello-^').stripRight('^[a-z]$').s === '[$]hello');
+
+        T (S(123).stripRight(3).s === '12');
+      });
+    });
+
     describe('+ restorePrototype()', function() {
       it('should restore the original String prototype', function() {
         T (typeof ' hi'.endsWith === 'undefined');