chore(TypeScript): refactor objects into classes

fix: `Nil`(null, undefined) now renders as empty string
change: `parser.parseValue()` renamed to `parser.parseOutput`
change: registered tags/filters become static and shared across different liquid instances

test/unit/util/error.ts

@@ -1,4 +1,4 @@
-import Liquid from '../../../src'
+import Liquid from '../../../src/liquid'
 import * as mock from 'mock-fs'
 import * as chai from 'chai'
 import * as path from 'path'

test/unit/util/promise.ts

@@ -4,7 +4,7 @@ const expect = chai.expect
 chai.use(require('chai-as-promised'))
 chai.use(require('sinon-chai'))
 
-const P = require('../../../src/util/promise.js')
+const P = require('../../../src/util/promise')
 
 describe('util/promise', function () {
   describe('.anySeries()', function () {

test/unit/util/strftime.ts

@@ -126,7 +126,7 @@ describe('util/strftime', function () {
 })
 
 function mockUTC () {
-  const p = Date.prototype
+  const p = Date.prototype as any
 
   p._getHours = p.getHours
   p.getHours = p.getUTCHours
@@ -139,7 +139,7 @@ function mockUTC () {
 }
 
 function restoreUTC () {
-  const p = Date.prototype
+  const p = Date.prototype as any
   p.getHours = p._getHours
   p.getDays = p._getDays
   p.getTimezoneOffset = p._getTimezoneOffset

test/unit/util/underscore.ts

@@ -21,7 +21,7 @@ describe('util/underscore', function () {
       expect(_.isError(new RenderError(new Error(), tpl))).to.be.true
     })
     it('should return true for RenderBreakError', function () {
-      expect(_.isError(new RenderBreakError())).to.be.true
+      expect(_.isError(new RenderBreakError(''))).to.be.true
     })
   })
   describe('.isString()', function () {
@@ -45,11 +45,11 @@ describe('util/underscore', function () {
     it('should recursively call toLiquid()', function () {
       expect(_.stringify({ toLiquid: () => ({ toLiquid: () => 'foo' }) })).to.equal('foo')
     })
-    it('should return "null" for null', function () {
-      expect(_.stringify(null)).to.equal('null')
+    it('should return "" for null', function () {
+      expect(_.stringify(null)).to.equal('')
     })
-    it('should return "undefined" for undefined', function () {
-      expect(_.stringify(undefined)).to.equal('undefined')
+    it('should return "" for undefined', function () {
+      expect(_.stringify(undefined)).to.equal('')
     })
     it('should return regex string for RegExp', function () {
       const reg = /foo/g
@@ -98,7 +98,7 @@ describe('util/underscore', function () {
     it('should return a range of integers', function () {
       expect(_.range(3, 5)).to.deep.equal([3, 4])
     })
-    it('should treat start as 0 if omitted', function () {
+    it('should start from 0 if begin omitted', function () {
       expect(_.range(3)).to.deep.equal([0, 1, 2])
     })
   })