Add promise support using universalify (#109)

Added new tests, refactored existing tests

Author: kartik2406

README.md

@@ -41,6 +41,15 @@ jsonfile.readFile(file, function(err, obj) {
 })
 ```
 
+You can also use this method with promises. The readFile() method will return a promise if you do not pass a callback function.
+
+```js
+var jsonfile = require('jsonfile')
+var file = '/tmp/data.json'
+jsonfile.readFile(file)
+  .then(obj => console.dir(obj)))
+  .catch(error => console.log(error));
+```
 
 ### readFileSync(filename, [options])
 
@@ -70,6 +79,21 @@ jsonfile.writeFile(file, obj, function (err) {
   console.error(err)
 })
 ```
+Or use with promises as follows:
+
+```js
+var jsonfile = require('jsonfile')
+
+var file = '/tmp/data.json'
+var obj = {name: 'JP'}
+
+jsonfile.writeFile(file, obj)
+  .then(res => {
+    console.log("Write complete");
+  })
+  .catch(error => console.log(error));
+```
+
 
 **formatting with spaces:**
 

index.js

@@ -4,15 +4,16 @@ try {
 } catch (_) {
   _fs = require('fs')
 }
+const universalify = require('universalify')
 
-function readFile (file, options, callback) {
+function readFileWithCallback (file, options, callback) {
   if (callback == null) {
     callback = options
     options = {}
   }
 
   if (typeof options === 'string') {
-    options = {encoding: options}
+    options = { encoding: options }
   }
 
   options = options || {}
@@ -44,10 +45,12 @@ function readFile (file, options, callback) {
   })
 }
 
+const readFile = universalify.fromCallback(readFileWithCallback)
+
 function readFileSync (file, options) {
   options = options || {}
   if (typeof options === 'string') {
-    options = {encoding: options}
+    options = { encoding: options }
   }
 
   var fs = options.fs || _fs
@@ -88,7 +91,7 @@ function stringify (obj, options) {
   return str.replace(/\n/g, EOL) + EOL
 }
 
-function writeFile (file, obj, options, callback) {
+function writeFileWithCallback (file, obj, options, callback) {
   if (callback == null) {
     callback = options
     options = {}
@@ -108,6 +111,8 @@ function writeFile (file, obj, options, callback) {
   fs.writeFile(file, str, options, callback)
 }
 
+const writeFile = universalify.fromCallback(writeFileWithCallback)
+
 function writeFileSync (file, obj, options) {
   options = options || {}
   var fs = options.fs || _fs

package.json

@@ -16,7 +16,9 @@
   ],
   "author": "JP Richardson <[email protected]>",
   "license": "MIT",
-  "dependencies": {},
+  "dependencies": {
+    "universalify": "^0.1.2"
+  },
   "optionalDependencies": {
     "graceful-fs": "^4.1.6"
   },

test/read-file-sync.test.js

@@ -23,7 +23,7 @@ describe('+ readFileSync()', function () {
 
   it('should read and parse JSON', function () {
     var file = path.join(TEST_DIR, 'somefile3.json')
-    var obj = {name: 'JP'}
+    var obj = { name: 'JP' }
     fs.writeFileSync(file, JSON.stringify(obj))
 
     try {
@@ -60,7 +60,7 @@ describe('+ readFileSync()', function () {
         jf.readFileSync(file)
       })
 
-      var obj = jf.readFileSync(file, {throws: false})
+      var obj = jf.readFileSync(file, { throws: false })
       assert.strictEqual(obj, null)
     })
   })
@@ -72,7 +72,7 @@ describe('+ readFileSync()', function () {
       fs.writeFileSync(file, data)
 
       assert.throws(function () {
-        jf.readFileSync(file, {throws: true})
+        jf.readFileSync(file, { throws: true })
       })
     })
   })
@@ -81,7 +81,7 @@ describe('+ readFileSync()', function () {
     it('should return null', function () {
       var file = path.join(TEST_DIR, 'somefile4-invalid.json')
 
-      var obj = jf.readFileSync(file, {throws: false})
+      var obj = jf.readFileSync(file, { throws: false })
       assert.strictEqual(obj, null)
     })
   })
@@ -91,7 +91,7 @@ describe('+ readFileSync()', function () {
       var file = path.join(TEST_DIR, 'somefile4-invalid.json')
 
       assert.throws(function () {
-        jf.readFileSync(file, {throws: true})
+        jf.readFileSync(file, { throws: true })
       })
     })
   })
@@ -111,7 +111,7 @@ describe('+ readFileSync()', function () {
       }
 
       fs.writeFileSync(file, JSON.stringify(obj))
-      var data = jf.readFileSync(file, {reviver: sillyReviver})
+      var data = jf.readFileSync(file, { reviver: sillyReviver })
       assert.strictEqual(data.name, 'jp')
       assert(data.day instanceof Date)
       assert.strictEqual(data.day.toISOString(), '2015-06-19T11:41:26.815Z')