feat(parser): more correct number parsing

This prevents strings with mixed numbers and strings to be parsed as numbers if
the string begins with a number. `123abc` will now evaluate to the string
instead of `123` with the previous parser.

index.js

@@ -189,7 +189,8 @@ module.exports.prototype.parseStringVal = function(string) {
     return true;
   } else if (this.string.toBoolean && string.toLowerCase() === 'false') {
     return false;
-  } else if (this.string.toNumber && !isNaN(parseFloat(string, 10))) {
+  } else if (this.string.toNumber && !isNaN(parseInt(string, 10)) &&
+      (+string - +string + 1) >= 0) {
     return parseFloat(string, 10);
   } else {
     return string;

test.js

@@ -132,6 +132,14 @@ describe('parseStringVal()', function() {
     assert.equal(qs.parseStringVal('000100'), 100);
   });
 
+  it('returns number for positive parseable integer', function() {
+    assert.equal(qs.parseStringVal('+100'), 100);
+  });
+
+  it('returns number for negative parseable integer', function() {
+    assert.equal(qs.parseStringVal('-100'), -100);
+  });
+
   it('returns number for parseable float', function() {
     assert.equal(qs.parseStringVal('10.123'), 10.123);
   });
@@ -140,9 +148,33 @@ describe('parseStringVal()', function() {
     assert.equal(qs.parseStringVal('00010.123'), 10.123);
   });
 
+  it('returns number for positive parseable float', function() {
+    assert.equal(qs.parseStringVal('+10.123'), 10.123);
+  });
+
+  it('returns number for negative parseable float', function() {
+    assert.equal(qs.parseStringVal('-10.123'), -10.123);
+  });
+
   it('returns string for empty string', function() {
     assert.equal(qs.parseStringVal(''), '');
   });
+
+  it('returns string for space string', function() {
+    assert.equal(qs.parseStringVal(' '), ' ');
+  });
+
+  it('returns string for "number string number"', function() {
+    assert.equal(qs.parseStringVal('123abc123'), '123abc123');
+  });
+
+  it('returns string for "string number"', function() {
+    assert.equal(qs.parseStringVal('abc123'), 'abc123');
+  });
+
+  it('returns string for "number string"', function() {
+    assert.equal(qs.parseStringVal('123abc'), '123abc');
+  });
 });
 
 describe('parseString()', function() {