diff --git a/API.md b/API.md
index d8157a5..0ab5b24 100644
--- a/API.md
+++ b/API.md
@@ -7,6 +7,10 @@
 
 ## camaro
 
+### `ready()`
+
+Initialize module. Needed to be called once before calling other methods.
+
 ### `transform(xml, template)`
 
 Transform xml string to JSON using the given template powered by XPath where:
@@ -44,6 +48,8 @@ const template = {
 
 ### `toJson(xml)`
 
+**Not yet implemented**
+
 Transform xml string to JSON where:
 - `xml` - the input xml string
 
diff --git a/README.md b/README.md
index 345a876..a2b61a5 100644
--- a/README.md
+++ b/README.md
@@ -76,7 +76,7 @@ The rest are pretty much vanilla XPath 1.0.
 For complete API documentation, please see [API.md](API.md)
 
 ```js
-const { transform, prettyPrint } = require('camaro')
+const { ready, transform, prettyPrint } = require('camaro')
 const fs = require('fs')
 
 const xml = fs.readFileSync('examples/ean.xml', 'utf-8')
@@ -99,6 +99,7 @@ const template = {
 }
 
 ;(async function () {
+    await ready()
     const result = await transform(xml, template)
     console.log(result)
 
diff --git a/index.js b/index.js
index 8f844e0..ca36c3b 100644
--- a/index.js
+++ b/index.js
@@ -9,22 +9,22 @@ function isEmptyObject(obj) {
 }
 
 let cachedInstance
-const instance = Module()
-instance.onRuntimeInitialized = () => {
-    cachedInstance = instance
-}
 
 function callWasmBinding(methodName, ...args) {
-    return new Promise((resolve) => {
+    if (!cachedInstance) throw new Error('camaro is not yet initialized. You need to call `ready()` first.')
+    return cachedInstance[methodName](...args)
+}
+
+const ready = () => {
+    return new Promise((resolve, reject) => {
         if (!cachedInstance) {
+            const instance = Module()
             instance.onRuntimeInitialized = () => {
                 cachedInstance = instance
-                const result = instance[methodName](...args)
-                resolve(result)
+                resolve()
             }
-        } else {
-            const result = cachedInstance[methodName](...args)
-            resolve(result)
+        } else {            
+            resolve()
         }
     })
 }
@@ -76,4 +76,4 @@ async function prettyPrint(xml, opts={indentSize: 2}) {
     return callWasmBinding('prettyPrint', xml, opts)
 }
 
-module.exports = { transform, toJson, prettyPrint }
\ No newline at end of file
+module.exports = { ready, transform, toJson, prettyPrint }
\ No newline at end of file
diff --git a/package.json b/package.json
index 5129344..09490b2 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "camaro",
-  "version": "4.2.0",
+  "version": "5.0.0",
   "description": "Transforming XML to JSON using Node.js binding to native pugixml parser library",
   "homepage": "https://github.com/tuananh/camaro",
   "bugs": "https://github.com/tuananh/camaro/issues",
diff --git a/test/array-in-array.test.js b/test/array-in-array.test.js
index d2b7fd3..872fb88 100644
--- a/test/array-in-array.test.js
+++ b/test/array-in-array.test.js
@@ -1,5 +1,5 @@
 const t = require('tape')
-const { transform } = require('../')
+const { ready, transform } = require('../')
 
 const xml = `
     <element>
@@ -30,7 +30,7 @@ t.test('array-in-array test .// should only match nodes inside current node', as
             items: ['.//item', '.']
         }]
     }
-
+    await ready()
     const result = await transform(xml, template)
 
     t.equal(result.elements[0].items.length, 3, 'elements[0].items should have only 3 elements')
diff --git a/test/array.test.js b/test/array.test.js
index b8e8bfe..be40879 100644
--- a/test/array.test.js
+++ b/test/array.test.js
@@ -1,6 +1,6 @@
 const fs = require('fs')
 const t = require('tape')
-const { transform } = require('../')
+const { ready, transform } = require('../')
 
 t.test('array test', async t => {
     const xml = fs.readFileSync('examples/recipe.xml', 'utf-8')
@@ -15,7 +15,7 @@ t.test('array test', async t => {
             }
         ]
     }
-
+    await ready()
     const result = await transform(xml, recipeTemplate)
     t.equal(typeof result, 'object', 'result is expected to be object')
     t.equal(result.id, 'moco09596c01s001r002')
diff --git a/test/basic.test.js b/test/basic.test.js
index 2710195..3b81112 100644
--- a/test/basic.test.js
+++ b/test/basic.test.js
@@ -1,6 +1,6 @@
 const fs = require('fs')
 const t = require('tape')
-const { transform } = require('../')
+const { ready, transform } = require('../')
 
 t.test('basic test', async (t) => {
     const xml = fs.readFileSync('examples/ean.xml', 'utf-8')
@@ -23,7 +23,7 @@ t.test('basic test', async (t) => {
         path_not_exist: '/HotelListResponse/nonExistenPath',
         empty_array: []
     }
-
+    await ready()
     const result = await transform(xml, template)
     t.equal(typeof result, 'object', 'result is expected to be object')
     t.equal(result.cache_key, '-48a4e19f:15bec159775:50eb', 'parse cache_key ok')
diff --git a/test/empty-path.test.js b/test/empty-path.test.js
index 110eb95..964b490 100644
--- a/test/empty-path.test.js
+++ b/test/empty-path.test.js
@@ -1,13 +1,12 @@
-const fs = require('fs')
 const t = require('tape')
-const { transform } = require('../')
+const { ready, transform } = require('../')
 
 t.test('empty path test', async t => {
     const xml = '<hello>world</hello>'
     const template = {
         empty: ''
     }
-
+    await ready()
     const result = await transform(xml, template)
     t.equal(result.empty,'','empty path => empty string')
     t.end()
diff --git a/test/function.test.js b/test/function.test.js
index 22d2cfb..006ab5b 100644
--- a/test/function.test.js
+++ b/test/function.test.js
@@ -1,5 +1,5 @@
 const t = require('tape')
-const { transform } = require('../')
+const { ready, transform } = require('../')
 const isWin = process.platform === 'win32'
 
 const xml = `
@@ -28,6 +28,7 @@ const xml = `
 `
 
 t.test('test function upper-case()', async (t) => {
+    await ready()
     const result = await transform(xml, {
         upperCase: ['//items/item', 'upper-case(.)']
     })
@@ -38,6 +39,7 @@ t.test('test function upper-case()', async (t) => {
 })
 
 t.test('test function lower-case()', async (t) => {
+    await ready()
     const result = await transform(xml, {
         lowerCase: ['//items/item', 'lower-case(.)']
     })
@@ -48,6 +50,7 @@ t.test('test function lower-case()', async (t) => {
 })
 
 t.test('test function title-case()', async (t) => {
+    await ready()
     const result = await transform(xml, {
         titleCase: ['//items/item', 'title-case(.)']
     })
@@ -58,6 +61,7 @@ t.test('test function title-case()', async (t) => {
 })
 
 t.test('test function title-case() unicode', async (t) => {
+    await ready()
     const result = await transform(xml, {
         titleCase: ['//unicode/item', 'title-case(.)']
     })
@@ -68,6 +72,7 @@ t.test('test function title-case() unicode', async (t) => {
 })
 
 t.test('test function title-case() upper after symbols', async (t) => {
+    await ready()
     const result = await transform(xml, {
         titleCase: ['//special/item', 'title-case(.)']
     })
@@ -78,6 +83,7 @@ t.test('test function title-case() upper after symbols', async (t) => {
 })
 
 t.test('test function camel-case()', async (t) => {
+    await ready()
     const result = await transform(xml, {
         camelCase: ['//items/item', 'camel-case(.)']
     })
@@ -88,6 +94,7 @@ t.test('test function camel-case()', async (t) => {
 })
 
 t.test('test function snake-case()', async (t) => {
+    await ready()
     const result = await transform(xml, {
         snakeCase: ['//items/item', 'snake-case(.)']
     })
@@ -98,6 +105,7 @@ t.test('test function snake-case()', async (t) => {
 })
 
 t.test('test nested function calls', async (t) => {
+    await ready()
     const result = await transform(xml, {
         snakeCase: ['//items/item', 'snake-case(lower-case(.))']
     })
@@ -108,36 +116,42 @@ t.test('test nested function calls', async (t) => {
 })
 
 t.test('test function round()', async (t) => {
+    await ready()
     const result = await transform(xml, { round: 'round(root/single)' })
     t.equal(result.round, 20)
     t.end()
 })
 
 t.test('test function floor()', async (t) => {
+    await ready()
     const result = await transform(xml, { floor: 'floor(root/single)' })
     t.equal(result.floor, 20)
     t.end()
 })
 
 t.test('test function ceiling()', async (t) => {
+    await ready()
     const result = await transform(xml, { ceiling: 'ceiling(root/single)' })
     t.equal(result.ceiling, 21)
     t.end()
 })
 
 t.test('test function sum()', async (t) => {
+    await ready()
     const result = await transform(xml, { sum: 'sum(root/number)' })
     t.equal(result.sum, 30.5)
     t.end()
 })
 
 t.test('test function count()', async (t) => {
+    await ready()
     const result = await transform(xml, { count: 'count(root/number)' })
     t.equal(result.count, 2)
     t.end()
 })
 
 t.test('test function boolean()', async (t) => {
+    await ready()
     const result = await transform(xml, {
         boolean: 'boolean(root/boolean = "TrUe")',
         boolean_false: 'boolean(root/boolean = "true")'
diff --git a/test/input.test.js b/test/input.test.js
index e36bdbc..c2692f3 100644
--- a/test/input.test.js
+++ b/test/input.test.js
@@ -1,9 +1,10 @@
 const t = require('tape')
-const { transform } = require('../')
+const { ready, transform } = require('../')
 
 t.test('test invalid xml string',async (t) => {
     try {
-        const result = await transform('', {})
+        await ready()
+        await transform('', {})
     } catch (err) {
         t.equal(err instanceof TypeError, true, 'should throw TypeError invalid xml string')
     }
@@ -13,13 +14,15 @@ t.test('test invalid xml string',async (t) => {
 
 t.test('test invalid template argument',async (t) => {
     try {
-        const result = await transform('<xml/>', null)
+        await ready()
+        await transform('<xml/>', null)
     } catch (err) {
         t.equal(err instanceof TypeError, true, 'should throw TypeError invalid template')
     }
 
     try {
-        const result = await transform('<xml/>', {})
+        await ready()
+        await transform('<xml/>', {})
     } catch (err) {
         t.equal(err instanceof TypeError, true, 'should throw TypeError invalid template')
     }
diff --git a/test/invalid-xpath.test.js b/test/invalid-xpath.test.js
index 28d3f21..f06e55f 100644
--- a/test/invalid-xpath.test.js
+++ b/test/invalid-xpath.test.js
@@ -1,13 +1,13 @@
 const fs = require('fs')
 const t = require('tape')
-const { transform } = require('../')
+const { ready, transform } = require('../')
 
 t.test('invalid xpath test', async t => {
     const xml = fs.readFileSync('examples/ean.xml', 'utf-8')
     const template = {
         invalidXPath: 'concat()'
     }
-
+    await ready()
     const result = await transform(xml, template)
     t.equal(result.invalidXPath, '')
     t.end()
diff --git a/test/output.test.js b/test/output.test.js
index 8f1f3d3..85f8455 100644
--- a/test/output.test.js
+++ b/test/output.test.js
@@ -1,15 +1,17 @@
 const t = require('tape')
-const { transform } = require('../')
+const { ready, transform } = require('../')
 
 t.test('test output is empty', async (t) => {
     try {
-        const result = await transform('Too Many Requests', { check: 'valid_xml' })
+        await ready()
+        await transform('Too Many Requests', { check: 'valid_xml' })
     } catch (err) {
         t.equal(err instanceof TypeError, true, 'should throw TypeError malformed xml')
     }
 
     try {
-        const result = await transform('<tag>invalid xml<ta/>', { check: 'valid_xml' })
+        await ready()
+        await transform('<tag>invalid xml<ta/>', { check: 'valid_xml' })
     } catch (err) {
         t.equal(err instanceof TypeError, true, 'should throw TypeError malformed xml')
     }
diff --git a/test/parallel.test.js b/test/parallel.test.js
new file mode 100644
index 0000000..849d4fb
--- /dev/null
+++ b/test/parallel.test.js
@@ -0,0 +1,13 @@
+const t = require('tape')
+const { ready, transform } = require('../')
+
+t.test('parallel test', async t => {
+    await ready()
+    const doit = () => transform('<foo>bar</foo>', { foo: 'foo' })
+    let called = 0
+    await doit().then(_ => { called += 1 })
+    await doit().then(_ => { called += 1 })
+
+    t.equal(called, 2, '`called` should equal to 2')
+    t.end()
+})
\ No newline at end of file
diff --git a/test/pretty-print.test.js b/test/pretty-print.test.js
index c388880..1dc92ec 100644
--- a/test/pretty-print.test.js
+++ b/test/pretty-print.test.js
@@ -1,9 +1,11 @@
 const fs = require('fs')
 const t = require('tape')
-const { prettyPrint } = require('../')
+const { ready, prettyPrint } = require('../')
+
+const xml = fs.readFileSync('examples/simple.xml', 'utf-8')
 
 t.test('pretty print default indentSize', async (t) => {
-    const xml = fs.readFileSync('examples/simple.xml', 'utf-8')
+    await ready()
     const prettyStr = await prettyPrint(xml)
     t.equal(prettyStr, `<root text="im root">
   <items>
@@ -17,7 +19,7 @@ t.test('pretty print default indentSize', async (t) => {
 })
 
 t.test('pretty print indentSize=4', async (t) => {
-    const xml = fs.readFileSync('examples/simple.xml', 'utf-8')
+    await ready()
     const prettyStr = await prettyPrint(xml, { indentSize: 4})
     t.equal(prettyStr, `<root text="im root">
     <items>
diff --git a/test/raw.test.js b/test/raw.test.js
index 27972a0..27945e3 100644
--- a/test/raw.test.js
+++ b/test/raw.test.js
@@ -1,6 +1,6 @@
 const fs = require('fs')
 const t = require('tape')
-const { transform } = require('..')
+const { ready, transform } = require('..')
 
 t.test('raw() test', async t => {
     const xml = fs.readFileSync('examples/simple.xml', 'utf-8')
@@ -10,6 +10,7 @@ t.test('raw() test', async t => {
         raw1: 'raw(root/items)',
         raw1NodeSet: 'raw(//item)'
     }
+    await ready()
     const result = await transform(xml, template)
 
     const rawXml = '<items>\n\t<item>1</item>\n\t<item>2</item>\n</items>\n'
diff --git a/test/ready.test.js b/test/ready.test.js
new file mode 100644
index 0000000..798e8e2
--- /dev/null
+++ b/test/ready.test.js
@@ -0,0 +1,16 @@
+const t = require('tape')
+
+// delete require cache to force module to reinitialize
+delete require.cache[require.resolve('../')]
+
+const { transform } = require('../')
+
+t.test('throw not ready error if `ready()` is not called', async t => {
+    try {
+        await transform('<foo>bar</foo>', { foo: 'foo' })
+        t.end()
+    } catch (err) {
+        t.equal(err.message, 'camaro is not yet initialized. You need to call `ready()` first.')        
+        t.end()
+    }
+})
\ No newline at end of file
diff --git a/test/template-is-array.test.js b/test/template-is-array.test.js
index 6c298ad..f64c4d8 100644
--- a/test/template-is-array.test.js
+++ b/test/template-is-array.test.js
@@ -1,8 +1,8 @@
 const t = require('tape')
-const { transform } = require('../')
+const { ready, transform } = require('../')
 
 t.test(
-    'camaro should be able to parse an array template too (1)',
+    'camaro should be able to parse an array template',
     async (t) => {
         const xml = `
             <root>
@@ -11,6 +11,7 @@ t.test(
                 <item>3</item>
             </root>
         `
+        await ready()
         const result = await transform(xml, ['root/item', 'number(.)'])
         t.deepEqual(result, [1, 2, 3])
 
diff --git a/test/template-key-order.test.js b/test/template-key-order.test.js
index f10d743..f53072e 100644
--- a/test/template-key-order.test.js
+++ b/test/template-key-order.test.js
@@ -1,5 +1,5 @@
 const t = require('tape')
-const { transform } = require('../')
+const { ready, transform } = require('../')
 
 const xml = `
     <root>
@@ -14,6 +14,7 @@ t.test('template key order test', async (t) => {
         'a': 'root/last_name',
         'c': 'root/middle_name'
     }
+    await ready()
     const output = await transform(xml, template)
     t.deepEqual(Object.keys(output), Object.keys(template), 'keys are in original order')