blocks|key|3401720|text|据我所知，没有内置的JavaScript函数具有相同的功能。不过，我认为最好的解决方案是按类而不是id查询，并使用dojo.forEach(...)因为您将在forEach闭包中保证有一个非空元素。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3401721|您可以始终使用JavaScript等效项：|3401722|dojo.byId('cool_input')+&&+dojo.byId('cool_input').whateverYouWantToDo(...);|code-block|syntax|javascript|3401723|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

As far as I know there isn't a built-in JavaScript function that has that same functionality. I think the best solution though is to query by class instead of id and use dojo.forEach(...) as you will be guaranteed a non-null element in the forEach closure.

You could always use the JavaScript equivalent:

<pre><code>dojo.byId('cool_input') &amp;&amp; dojo.byId('cool_input').whateverYouWantToDo(...);
</code></pre>

blocks|key|960159|text|我从未使用过dojo，但大多数javascript框架(在处理DOM时)在从element对象调用方法时都会返回调用元素(很糟糕，抱歉)。所以andand()是隐式的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|960160|dojo.addOnLoad(function()+{
++dojo.byId('cool_input').onkeyup(function(evt)+{+/*event+handler+code*/
++});
});|code-block|syntax|javascript|960161|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've never used dojo, but most javascript frameworks (when dealing with the DOM) return the calling element when a method is called from the element object (poor wording, sorry). So andand() would be implicit.

<pre><code>dojo.addOnLoad(function() {
 dojo.byId('cool_input').onkeyup(function(evt) { /*event handler code*/
 });
});
</code></pre>

blocks|key|3401766|text|这样如何：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3401767|function+andand(elt,+f)+{
++if+(elt)
++++return+f(elt);
++return+null;
}|code-block|syntax|javascript|3401768|像这样调用：|3401769|andand(dojo.byId('cool_input'),+function(elt)+{
++//+this+function+gets+called+with+elt+=+the+input+iff+it+exists
++dojo.addOnLoad(function()+{
++++elt.onkeyup+=+function()+{+...+};
++});
});|3401770|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|$]]

How about something like this:

<pre><code>function andand(elt, f) {
 if (elt)
 return f(elt);
 return null;
}
</code></pre>

Call like this:

<pre><code>andand(dojo.byId('cool_input'), function(elt) {
 // this function gets called with elt = the input iff it exists
 dojo.addOnLoad(function() {
 elt.onkeyup = function() { ... };
 });
});
</code></pre>

blocks|key|960185|text|我不知道Dojo，但是您的第一个示例不应该是这样的吗|type|unstyled|depth|inlineStyleRanges|entityRanges|data|960186|dojo.addOnLoad(function()+{
++++var+coolInput+=+dojo.byId('cool_input');
++++if(coolInput)
++++++++coolInput.onkeyup+=+function()+{+...+};
});|code-block|syntax|javascript|960187|否则，您最终可能会在构建DOM之前尝试访问该元素。|960188|回到您的问题:在JavaScript中，我将andand()实现为|offset|length|style|CODE|960189|function+andand(obj,+func,+args)+{
++++return+obj+&&+func.apply(obj,+args+%7C%7C+[]);
}|960190|然后，您的示例可以编写为|960191|dojo.addOnLoad(function()+{
++++andand(dojo.byId('cool_input'),+function()+{
++++++++this.onkeyup+=+function()+{+...+};
++++});
});|960192|这并不比使用显式的if语句短多少-所以为什么要麻烦呢？|960193|entityMap^0|0|0|0|M|8|0|0|0|0|9|2|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|10|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|11|8|@$K|12|L|13|M|N]]|9|@]|A|$]]|$1|O|3|P|5|D|7|14|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|15|8|@]|9|@]|A|$]]|$1|S|3|T|5|D|7|16|8|@]|9|@]|A|$E|F]]|$1|U|3|V|5|6|7|17|8|@$K|18|L|19|M|N]]|9|@]|A|$]]|$1|W|3|-4|5|6|7|1A|8|@]|9|@]|A|$]]]|X|$]]

I don't know Dojo, but shouldn't your first example read

<pre><code>dojo.addOnLoad(function() {
 var coolInput = dojo.byId('cool_input');
 if(coolInput)
 coolInput.onkeyup = function() { ... };
});
</code></pre>

Otherwise, you might end up trying to access the element before the DOM has been built.

Back to your question: In JavaScript, I'd implement <code>andand()</code> as

<pre><code>function andand(obj, func, args) {
 return obj &amp;&amp; func.apply(obj, args || []);
}
</code></pre>

Your example could then be written as

<pre><code>dojo.addOnLoad(function() {
 andand(dojo.byId('cool_input'), function() {
 this.onkeyup = function() { ... };
 });
});
</code></pre>

which isn't really that much shorter than using the explicit <code>if</code> statement - so why bother?

blocks|key|960207|text|查看列表：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|960208|Array.prototype.andand+=+function(property,+fn)+{

++++if+(this.filter(property).length+>+0)+this.map(fn);
}|code-block|syntax|javascript|960209|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|$]]

For a list:

<pre><code>Array.prototype.andand = function(property, fn) {

 if (this.filter(property).length &gt; 0) this.map(fn);
}
</code></pre>

blocks|key|3401918|text|您想要的确切语法在JavaScript中是不可能的。JavaScript的执行方式需要以一种非常基本的方式进行更改。例如：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3401919|var+name+=+getUserById(id).andand().name;
//++++++++++++++++++++++++%5E
//++++++++++++++++++++++++%7C-------------------------------
//+if+getUserById+returns+null,+execution+MUST+stop+here+%7C
//+otherwise,+you'll+get+a+"null+is+not+an+object"+exception|code-block|syntax|javascript|3401920|然而，JavaScript不是这样工作的。它根本就不是。|3401921|下面这行代码执行的几乎就是您想要的。|3401922|var+name+=+(var+user+=+getUserById(id))+?+user.name+:+null;|3401923|但是可读性不能扩展到更大的例子。例如：|3401924|//+this+is+what+you+want+to+see
var+initial+=+getUserById(id).andand().name.andand()[0];
//+this+is+the+best+that+JavaScript+can+do
var+initial+=+(var+name+=+(var+user+=+getUserById(id))+?+user.name+:+null)+?+name[0]+:+null;|3401925|而且这些不必要的变量也有副作用。我使用这些变量来避免重复查找。变量搞乱了上下文，如果这是个大问题，你可以使用匿名函数：|3401926|var+name+=+(function()+{return+(var+user+=+getUserById(id))+?+user.name+:+null;})();|3401927|现在，user变量被正确地清除了，每个人都很高兴。但是哇！打字太多了！:)|3401928|entityMap^0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|10|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|11|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|12|8|@]|9|@]|A|$E|F]]|$1|M|3|N|5|6|7|13|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|14|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|15|8|@]|9|@]|A|$]]|$1|S|3|T|5|D|7|16|8|@]|9|@]|A|$E|F]]|$1|U|3|V|5|6|7|17|8|@]|9|@]|A|$]]|$1|W|3|-4|5|6|7|18|8|@]|9|@]|A|$]]]|X|$]]

The exact syntax you want is not possible in JavaScript. The way JavaScript executes would need to change in a pretty fundamental fashion. For example:

<pre><code>var name = getUserById(id).andand().name;
// ^
// |-------------------------------
// if getUserById returns null, execution MUST stop here |
// otherwise, you'll get a "null is not an object" exception
</code></pre>

However, JavaScript doesn't work that way. It simply doesn't.

The following line performs almost exactly what you want.

<pre><code>var name = (var user = getUserById(id)) ? user.name : null;
</code></pre>

But readability won't scale to larger examples. For example:

<pre><code>// this is what you want to see
var initial = getUserById(id).andand().name.andand()[0];
// this is the best that JavaScript can do
var initial = (var name = (var user = getUserById(id)) ? user.name : null) ? name[0] : null;
</code></pre>

And there is the side-effect of those unnecessary variables. I use those variables to avoid the double lookup. The variables are mucking up the context, and if that's a huge deal, you can use anonymous functions:

<pre><code>var name = (function() {return (var user = getUserById(id)) ? user.name : null;})();
</code></pre>

Now, the user variable is cleaned-up properly, and everybody's happy. But wow! what a lot of typing! :)

blocks|key|4249022|text|你想要dojo.behavior。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4249023|dojo.behavior.add({
++++'#cool_input':+{
++++++++onKeyUp:+function(evt)+{+...+}
++++}
});|code-block|syntax|javascript|4249024|entityMap|0|LINK|mutability|MUTABLE|url|http://dojocampus.org/content/2008/03/26/cleaning-your-markup-with-dojobehavior/^0|3|D|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

You want <a href="http://dojocampus.org/content/2008/03/26/cleaning-your-markup-with-dojobehavior/" rel="nofollow noreferrer">dojo.behavior</a>.

<pre><code>dojo.behavior.add({
 '#cool_input': {
 onKeyUp: function(evt) { ... }
 }
});
</code></pre>

In trying to make my Javascript unobtrusive, I'm using <code>onLoad</code>s to add functionality to <code>&lt;input&gt;</code>s and such. With Dojo, this looks something like:

<pre><code>var coolInput = dojo.byId('cool_input');
if(coolInput) {
 dojo.addOnLoad(function() {
 coolInput.onkeyup = function() { ... };
 });
}
</code></pre>

Or, approximately equivalently:

<pre><code>dojo.addOnLoad(function() {
 dojo.forEach(dojo.query('#cool_input'), function(elt) {
 elt.onkeyup = function() { ... };
 });
});
</code></pre>

Has anyone written an implementation of Ruby's <a href="http://github.com/raganwald/andand/tree/master" rel="noreferrer">andand</a> so that I could do the following?

<pre><code>dojo.addOnLoad(function() {
 // the input's onkeyup is set iff the input exists
 dojo.byId('cool_input').andand().onkeyup = function() { ... };
});
</code></pre>

or

<pre><code>dojo.byId('cool_input').andand(function(elt) {
 // this function gets called with elt = the input iff it exists
 dojo.addOnLoad(function() {
 elt.onkeyup = function() { ... };
 });
});
</code></pre>

Is there a Javascript equivalent of Ruby's andand?

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。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

为了让我的Javascript变得不那么引人注目，我使用了onLoads来给Javascript s等等添加功能。在Dojo中，这看起来类似于：var coolInput = dojo.byId('cool_input');if(coolInput) {  dojo.addOnLoad(function() {    ...

问有没有相当于Ruby的andand的Javascript？
EN

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问有没有相当于Ruby的andand的Javascript？EN