blocks|key|1989462|text|直接使用Object.assign无法实现这一点，因为每个下一个对象都会为prev重写相同的键。唯一的方法是使用手工构建的函数过滤传入的对象。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1989463|function+filterObject(obj)+{
++++const+ret+=+{};
++++Object.keys(obj)
++++++++.filter((key)+=>+obj[key]+!==+undefined)
++++++++.forEach((key)+=>+ret[key]+=+obj[key]);
++++return+ret;
}|code-block|syntax|javascript|1989464|entityMap^0|4|D|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

You can't achieve that with a straight usage of <code>Object.assign</code>, because each next object will rewrite the same keys for prev merge. The only way, to filter your incoming objects with some hand-crafted function.

<pre><code>function filterObject(obj) {
 const ret = {};
 Object.keys(obj)
 .filter((key) =&gt; obj[key] !== undefined)
 .forEach((key) =&gt; ret[key] = obj[key]);
 return ret;
}
</code></pre>

blocks|key|1990094|text|在传递给undefined值之前，您可以简单地过滤出带有Object.assign()值的键。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1990095|​|1990096|const+assign+=+(target,+...sources)+=>
++Object.assign(target,+...sources.map(x+=>
++++Object.entries(x)
++++++.filter(([key,+value])+=>+value+!==+undefined)
++++++.reduce((obj,+[key,+value])+=>+(obj[key]+=+value,+obj),+{})
++))

console.log(assign({},+{key:+2},+{key:+undefined}))|code-block|syntax|javascript|1990097|1990098|entityMap^0|4|9|S|F|0|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|U|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|V|8|@]|D|@]|E|$K|L]]|$1|M|3|G|5|6|7|W|8|@]|D|@]|E|$]]|$1|N|3|-4|5|6|7|X|8|@]|D|@]|E|$]]]|O|$]]

You can simply filter out the keys with <code>undefined</code> values before passing them to <code>Object.assign()</code>:

<div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>const assign = (target, ...sources) =&gt;
 Object.assign(target, ...sources.map(x =&gt;
 Object.entries(x)
 .filter(([key, value]) =&gt; value !== undefined)
 .reduce((obj, [key, value]) =&gt; (obj[key] = value, obj), {})
 ))

console.log(assign({}, {key: 2}, {key: undefined}))</code></pre>
</div>
</div>

blocks|key|3455380|text|编写一个小实用程序来删除未定义的值：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3455381|function+removeUndefined(obj)+{
++for+(let+k+in+obj)+if+(obj[k]+===+undefined)+delete+obj[k];
++return+obj;
}|code-block|syntax|javascript|3455382|然后|3455383|Object.assign({},+{key:+2},+removeUndefined({key:+undefined}))|3455384|这似乎比用有线方式编写自己的assign更好，以删除未定义的值。|offset|length|style|CODE|3455385|entityMap^0|0|0|0|0|E|6|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

Write a little utility to remove undefined values:

<pre><code>function removeUndefined(obj) {
 for (let k in obj) if (obj[k] === undefined) delete obj[k];
 return obj;
}
</code></pre>

Then

<pre><code>Object.assign({}, {key: 2}, removeUndefined({key: undefined}))
</code></pre>

This seems preferable to writing your own <code>assign</code> with wired-in behavior to remove undefined values.

blocks|key|1990113|text|使用combine省略零值，然后通过扩展将两个对象组合为一个。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1990114|{+...(omitBy({key:+2},+isNil)),+...(omitBy({key:+undefined},+isNil))}|code-block|syntax|javascript|1990115|请参阅有关https://lodash.com/docs/4.17.15的更多信息|offset|length|1990116|entityMap|0|LINK|mutability|MUTABLE|url|https://lodash.com/docs/4.17.15^0|0|0|5|V|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

use lodash to omit nil values and then combine the two objects into one via spread
<pre><code>{ ...(omitBy({key: 2}, isNil)), ...(omitBy({key: undefined}, isNil))}
</code></pre>
See more info on lodash here <a href="https://lodash.com/docs/4.17.15" rel="nofollow noreferrer">https://lodash.com/docs/4.17.15</a>

blocks|key|3455417|text|使用be+2019/be+10的新对象方法，Object.fromEntries()、Michał的answer可以更新：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3455418|const+assign+=+(target,+...sources)+=>
++Object.assign(target,+...sources.map(x+=>
++++Object.fromEntries(
++++++Object.entries(x)
++++++++.filter(([key,+value])+=>+value+!==+undefined)
++++)
++))

console.log(assign({},+{key:+2},+{key:+undefined}))|code-block|syntax|javascript|3455419|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/fromEntries|1|https://stackoverflow.com/a/39977764/2379762^0|M|K|M|K|0|1E|6|1|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@$9|X|A|Y|1|Z]|$9|10|A|11|1|12]]|E|$]]|$1|F|3|G|5|H|7|13|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|L|$M|$5|N|O|P|E|$Q|R]]|S|$5|N|O|P|E|$Q|T]]]]

With ES2019/ES10's new object method, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/fromEntries" rel="nofollow noreferrer"><code>Object.fromEntries()</code></a>, Michał's <a href="https://stackoverflow.com/a/39977764/2379762">answer</a> can be updated:
<pre><code>const assign = (target, ...sources) =&gt;
 Object.assign(target, ...sources.map(x =&gt;
 Object.fromEntries(
 Object.entries(x)
 .filter(([key, value]) =&gt; value !== undefined)
 )
 ))

console.log(assign({}, {key: 2}, {key: undefined}))
</code></pre>

blocks|key|1989508|text|如果只需要值而不需要对象，也可以使用对象析构：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1989509|const+input+=+{+a:+0,+b:+"",+c:+false,+d:+null,+e:+undefined+};
const+{+a+=+1,+b+=+2,+c+=+3,+d+=+4,+e+=+5,+f+=+6+}+=+input;
console.log(a,+b,+c,+d,+e,+f);
//+=>+0,+"",+false,+null,+5,+6|code-block|syntax|javascript|1989510|这只会覆盖缺失或未定义的值。|1989511|我经常将它用于函数参数默认值，如下所示：|1989512|function+f(options+=+{})+{
++const+{+foo+=+42,+bar+}+=+options;
++console.log(foo,+bar);
}

f();
//+=>+42,+undefined

f({})
//+=>+42,+undefined

f({+foo:+123+})
//+=>+123,+undefined

f({+bar:+567+})
//+=>+42,+567

f({+foo:+123,+bar:+567+})
//+=>+123,+567|1989513|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

If you just need the values and don't need an object, you could also use object destructuring:
<pre class="lang-js prettyprint-override"><code>const input = { a: 0, b: &quot;&quot;, c: false, d: null, e: undefined };
const { a = 1, b = 2, c = 3, d = 4, e = 5, f = 6 } = input;
console.log(a, b, c, d, e, f);
// =&gt; 0, &quot;&quot;, false, null, 5, 6
</code></pre>
This will only override absent or undefined values.
I often use this for function argument default values like this:
<pre class="lang-js prettyprint-override"><code>function f(options = {}) {
 const { foo = 42, bar } = options;
 console.log(foo, bar);
}

f();
// =&gt; 42, undefined

f({})
// =&gt; 42, undefined

f({ foo: 123 })
// =&gt; 123, undefined

f({ bar: 567 })
// =&gt; 42, 567

f({ foo: 123, bar: 567 })
// =&gt; 123, 567
</code></pre>

There is <a href="https://stackoverflow.com/questions/19965844/lodash-difference-between-extend-assign-and-merge?noredirect=1&amp;lq=1">_.merge</a> functionality in lodash. I want to achieve the same thing in ES6 or ES7.

Having this snippet:

<pre><code>Object.assign({}, {key: 2}, {key: undefined})
</code></pre>

I want to receive <code>{key: 2}</code>. Currently I receive <code>{key: undefined}</code>

This is NOT a deep merge.

Is it possible? If yes then how to achieve that?

(_.merge in ES6/ES7)Object.assign without overriding undefined values

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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在存档中有功能。我想在ES6或ES7中实现同样的目标。有这样的片段：Object.assign({}, {key: 2}, {key: undefined})我想接收{key: 2}。目前我收到{key: undefined}这是而不是深度合并。有可能吗？如果是，那如何实现这一目标？

问(ES6/ES7中的_.merge)Object.assign而不覆盖未定义的值
EN

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问(ES6/ES7中的_.merge)Object.assign而不覆盖未定义的值EN