blocks|key|495503|text|observableArray公开了一个indexOf函数(ko.utils.arrayIndexOf的包装器)。这允许您执行以下操作：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|495504|if+(myObservableArray.indexOf(itemToAdd)+<+0)+{
++myObservableArray.push(itemToAdd);
}|code-block|syntax|javascript|495505|如果这两者实际上不是对同一对象的引用，并且您希望运行自定义比较逻辑，则可以使用ko.utils.arrayFirst，如下所示：|495506|var+match+=+ko.utils.arrayFirst(myObservableArray(),+function(item)+{
++++return+itemToAdd.id+===+item.id;
});

if+(!match)+{
++myObservableArray.push(itemToAdd);
}|495507|entityMap^0|K|7|U|L|0|0|13|J|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|10|8|@]|D|@]|E|$]]]|P|$]]

An observableArray exposes an <code>indexOf</code> function (wrapper to <code>ko.utils.arrayIndexOf</code>). This allows you to do:

<pre><code>if (myObservableArray.indexOf(itemToAdd) &lt; 0) {
 myObservableArray.push(itemToAdd);
}
</code></pre>

If the two are not actually a reference to the same object and you want to run custom comparison logic, then you can use <code>ko.utils.arrayFirst</code> like:

<pre><code>var match = ko.utils.arrayFirst(myObservableArray(), function(item) {
 return itemToAdd.id === item.id;
});

if (!match) {
 myObservableArray.push(itemToAdd);
}
</code></pre>

blocks|key|495526|text|谢谢RP。下面是一个使用您的建议从我的视图模型中通过对象的'id‘属性返回'name’属性的示例。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|495527|++++self.jobroles+=+ko.observableArray([]);

++++self.jobroleName+=+function+(id)
++++{
++++++++var+match+=+ko.utils.arrayFirst(self.jobroles(),+function+(item)
++++++++{
++++++++++++return+item.id()+===+id();++//note+the+()
++++++++});
++++++++if+(!match)
++++++++++++return+'error';
++++++++else
++++++++++++return+match.name;
++++};|code-block|syntax|javascript|495528|在超文本标记语言中，我有以下内容($parent是因为它在一个表行循环中)：|495529|<select+data-bind="visible:+editing,+hasfocus:+editing,+options:+$parent.jobroles,+optionsText:+'name',+optionsValue:+'id',+value:+jobroleId,+optionsCaption:+'--+Select+--'">
++++++++++++++++++++++++++++</select>
<span+data-bind="visible:+!editing(),+text:+$parent.jobroleName(jobroleId),+click:+edit"></td>|495530|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Thanks RP. Here's an example of using your suggestion to return the 'name' property via the object's 'id' property from within my view model.

<pre><code> self.jobroles = ko.observableArray([]);

 self.jobroleName = function (id)
 {
 var match = ko.utils.arrayFirst(self.jobroles(), function (item)
 {
 return item.id() === id(); //note the ()
 });
 if (!match)
 return 'error';
 else
 return match.name;
 };
</code></pre>

In HTML, i have the following ($parent is due to this being inside a table row loop):

<pre><code>&lt;select data-bind="visible: editing, hasfocus: editing, options: $parent.jobroles, optionsText: 'name', optionsValue: 'id', value: jobroleId, optionsCaption: '-- Select --'"&gt;
 &lt;/select&gt;
&lt;span data-bind="visible: !editing(), text: $parent.jobroleName(jobroleId), click: edit"&gt;&lt;/span&gt;&lt;/td&gt;
</code></pre>

blocks|key|710934|text|我会在更改之前添加"valueWillMutate()“，在更改之后添加"valueHasMutated()”。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|710935|for+(var+i+=+0;+i+<+data.length;+i%2B%2B)+{
++++var+needChange+=+false;
++++var+itemToAdd+=+data[i];
++++var+match+=+ko.utils.arrayFirst(MyArray(),+function+(item)+{
++++++++return+(itemToAdd.Code+===+item.Code);
++++});
++++if+(!match+&&+!needChange)+{
++++++++MyArray.valueWillMutate();
++++++++needChange+=+true;
++++}
++++if+(!match)+{
++++++++MyArray.push(itemToAdd);
++++}
}
if+(needChange)+{
++++MyArray.valueHasMutated();
}|code-block|syntax|javascript|710936|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I would add "valueWillMutate()" before changes and "valueHasMutated()" after them.

<pre><code>for (var i = 0; i &lt; data.length; i++) {
 var needChange = false;
 var itemToAdd = data[i];
 var match = ko.utils.arrayFirst(MyArray(), function (item) {
 return (itemToAdd.Code === item.Code);
 });
 if (!match &amp;&amp; !needChange) {
 MyArray.valueWillMutate();
 needChange = true;
 }
 if (!match) {
 MyArray.push(itemToAdd);
 }
}
if (needChange) {
 MyArray.valueHasMutated();
}
</code></pre>

I would like to <code>push</code> a new item onto an <code>observableArray</code>, but only if the item is not already present. Is there any "find" function or recommended pattern for achieving this in KnockoutJS?

I've noticed that the <code>remove</code> function on an <code>observableArray</code> can receive a function for passing in a condition. I almost want the same functionality, but to only push it if the condition passed in is or is not true.

How to conditionally push an item in an observable array?

我想要将一个新项目push到observableArray上，但前提是该项目不存在。在KnockoutJS中有什么“查找”功能或推荐的模式来实现这一点吗？我注意到observableArray上的remove函数可以接收传入条件的函数。我几乎想要相同的功能，但只在传入的条件为真或不为真时才推送它。

问如何有条件地推送可观察数组中的项？
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