Support editor to return PromiseLike object (#48)

README.md

@@ -96,7 +96,7 @@ This object is passed to deepmerge as its [option](https://github.com/TehShrike/
 #### editorFunction
 Type: `function`
 
-The `editorFunction` must have the following signature: `function (json) {}`, and must return JSON object.
+The `editorFunction` must have the following signature: `function (json) {}`, and must return JSON object or PromiseLike object with JSON object as value.
 
 #### jsBeautifyOptions
 Type: `object`

index.js

@@ -36,6 +36,7 @@ module.exports = function(editor, jsbeautifyOptions, deepmergeOptions) {
    * create through object and return it
    */
   return through.obj(function(file, encoding, callback) {
+    var self = this;
 
     // ignore it
     if (file.isNull()) {
@@ -50,6 +51,12 @@ module.exports = function(editor, jsbeautifyOptions, deepmergeOptions) {
       return callback();
     }
 
+    // when edit fail
+    var onError = function(err) {
+      self.emit('error', new PluginError('gulp-json-editor', err));
+      callback();
+    };
+
     try {
       // try to get current indentation
       var indent = detectIndent(file.contents.toString('utf8'));
@@ -60,21 +67,34 @@ module.exports = function(editor, jsbeautifyOptions, deepmergeOptions) {
       beautifyOptions.indent_char = beautifyOptions.indent_char || (indent.type === 'tab' ? '\t' : ' ');
       beautifyOptions.beautify = !('beautify' in beautifyOptions && !beautifyOptions.beautify);
 
+      // when edit success
+      var onSuccess = function(json) {
+        json = JSON.stringify(json);
+
+        // beautify JSON
+        if (beautifyOptions.beautify) {
+          json = jsbeautify(json, beautifyOptions);
+        }
+
+        // write it to file
+        file.contents = Buffer.from(json);
+        self.push(file);
+        callback();
+      };
+
       // edit JSON object and get it as string notation
-      var json = JSON.stringify(editBy(JSON.parse(file.contents.toString('utf8'))));
-
-      // beautify JSON
-      if (beautifyOptions.beautify) {
-        json = jsbeautify(json, beautifyOptions);
+      var res = editBy(JSON.parse(file.contents.toString('utf8')));
+      if (isPromiseLike(res)) {
+        res.then(onSuccess, onError);
+      } else {
+        onSuccess(res);
       }
-
-      // write it to file
-      file.contents = Buffer.from(json);
     } catch (err) {
-      this.emit('error', new PluginError('gulp-json-editor', err));
+      onError(err);
     }
-
-    this.push(file);
-    callback();
   });
 };
+
+function isPromiseLike(maybePromise) {
+  return typeof maybePromise === 'object' && maybePromise !== null && typeof maybePromise.then === 'function';
+}

test/byFunction.js

@@ -172,3 +172,29 @@ it('should multiple properties of JSON object (by function editor)', function(do
     done();
   });
 });
+
+
+it('should modify property asynchronous', function(done) {
+
+  var stream = gulp
+    .src('test/test.json')
+    .pipe(json(function(obj) {
+      obj.version = '2.0.0';
+      return Promise.resolve(obj);
+    }));
+
+  stream.on('data', function(file) {
+    var expected =
+      '{\n' +
+      '  "name": "test object",\n' +
+      '  "version": "2.0.0",\n' +
+      '  "nested": {\n' +
+      '    "name": "nested object",\n' +
+      '    "version": "1.0.0"\n' +
+      '  },\n' +
+      '  "authors": ["tom"]\n' +
+      '}';
+    file.contents.toString().should.eql(expected);
+    done();
+  });
+});

test/error.js

@@ -2,6 +2,7 @@ var json   = require('../');
 var fs     = require('fs');
 var File   = require('vinyl');
 var should = require('should');
+var gulp   = require('gulp');
 
 it('should raise error when missing option', function(done) {
   should(function() {json();}).throw('missing "editor" option');
@@ -36,3 +37,19 @@ it('should raise error when streaming input', function(done) {
       contents: fs.createReadStream('test/test.json'),
     }));
 });
+
+
+it('should raise error when Promise.reject', function(done) {
+  var msg = 'throw error in async editor';
+  gulp
+    .src('test/test.json')
+    .pipe(
+      json(function () {
+        return Promise.reject(new Error(msg));
+      })
+    )
+    .on('error', function (err) {
+      err.message.should.equal(msg);
+      done();
+    });
+});