Add "exists" function to "fs" module

fs.js

@@ -16,6 +16,20 @@ var path = require('path')
  * @module
  */
 module.exports = {
+  /**
+   * Custom implementation of [q-io/fs#exists](http://documentup.com/kriskowal/q-io#lexistsPath)
+   * to avoid dependency on q-io
+   * @param {string} existsPath the path to check
+   * @returns {Promise<boolean>} a promise for the existance (true/false) of the file/dir at the path
+   */
+  exists: function list (existsPath) {
+    return new Q.Promise(function (resolve, reject) {
+      fs.access(existsPath, function (err) {
+        resolve(!err)
+      })
+    })
+  },
+
   /**
    * Custom implementation of [q-io/fs#listTree](http://documentup.com/kriskowal/q-io#listtreepath-guardpath-stat)
    * to avoid dependency on q-io

test/fs-spec.js

@@ -27,6 +27,20 @@ describe('m-io/fs', function () {
     return x.sort()
   }
 
+  describe('the exists function', function () {
+    it('should return true if dir path exists', function () {
+      return mfs.exists('test/fixtures/dir').should.eventually.equal(true)
+    })
+
+    it('should return true if file path exists', function () {
+      return mfs.exists('test/fixtures/dir/file.txt').should.eventually.equal(true)
+    })
+
+    it('should return false if dir path does not exist', function () {
+      return mfs.exists('test/fixtures/no-dir-or-file').should.eventually.equal(false)
+    })
+  })
+
   describe('the list function', function () {
     it('should list all entries in a directory', function () {
       return mfs.list('test/fixtures/dir').then(sort).should.eventually.deep.equal([