fix(utils): deepMixIn to properly merge undefined values of source (#502)

ivanvoznyakovsky · crobinson42 · commit 2fb5bf09a3e1 · 2018-06-22T15:23:20.000-07:00
diff --git a/src/utils.js b/src/utils.js
@@ -409,7 +409,7 @@ const utils = {
         const existing = dest[key]
         if (isPlainObject(value) && isPlainObject(existing)) {
           utils.deepMixIn(existing, value)
-        } else {
+        } else if (existing === undefined || value !== undefined) {
           dest[key] = value
         }
       }
diff --git a/test/unit/utils/extendUtils.test.js b/test/unit/utils/extendUtils.test.js
@@ -54,6 +54,15 @@ describe('utils.deepMixIn', function () {
     assert.deepEqual(expected, actual, 'sorce own properties recursivly copied and overriden into dest')
     assert.equal(dest, utils.deepMixIn(dest), 'empty source argument returns dest')
   })
+
+  it('skips source properties that resolve to undefined if a destination value exists', function () {
+    const dest = { name: 'John', age: 90 }
+    const src = { name: 'John', age: undefined }
+    const expected = { name: 'John', age: 90 }
+    const actual = utils.deepMixIn(dest, src)
+
+    assert.deepEqual(expected, actual)
+  })
 })
 
 describe('utils.extend', function () {

Original file line number	Diff line number	Diff line change
`@@ -409,7 +409,7 @@ const utils = {`
`409`	`409`	`const existing = dest[key]`
`410`	`410`	`if (isPlainObject(value) && isPlainObject(existing)) {`
`411`	`411`	`utils.deepMixIn(existing, value)`
`412`		`- } else {`
	`412`	`+ } else if (existing === undefined \|\| value !== undefined) {`
`413`	`413`	`dest[key] = value`
`414`	`414`	`}`
`415`	`415`	`}`