add identifier keyword

escape.js

@@ -1,6 +1,7 @@
 'use strict';
 
 const _ = require('lodash');
+const identifier = require('./identifier');
 
 var escape = function(s, noquote)
 {
@@ -11,6 +12,12 @@ var escape = function(s, noquote)
       return `'${s.replace(/\'/g, "''")}'`;
     }
   }
+  if(s instanceof identifier) {
+    return escape(s.toString(), true);
+  }
+  if(_.isNull(s)) {
+    return 'null';
+  }
   if(_.isArray(s)) {
     var els = _.map(s, function(el) {
       return `${escape(el)}`;

identifier.js

@@ -0,0 +1,15 @@
+'use strict';
+
+var Identifier = function(s)
+{
+  this.s = s;
+  return this;
+};
+
+Identifier.prototype.toString = function()
+{
+  return this.s.toString();
+};
+
+module.exports = Identifier;
+

spec/escape_spec.js

@@ -1,6 +1,7 @@
 'use strict';
 
 const escape = require('../escape');
+const identifier = require('../identifier');
 
 describe('escape value tests', function() {
   
@@ -16,6 +17,10 @@ describe('escape value tests', function() {
     expect(escape(3.1)).toEqual('3.1');
   });
 
+  it('should escape null', function() {
+    expect(escape(null)).toEqual('null');
+  });
+
   it('should escape [1,\'2\']', function() {
     expect(escape([1,'2'])).toEqual('[1,\'2\']');
   });
@@ -28,5 +33,9 @@ describe('escape value tests', function() {
     expect(escape({a:'\'text\'',b:{c:6,d:'\'string\''}})).toEqual('{a:\'\'\'text\'\'\',b:{c:6,d:\'\'\'string\'\'\'}}');
   });
 
+  it('should escape identifier(\'a\')', function() {
+    expect(escape(new identifier('a'))).toEqual('a');
+  });
+
 });