blocks|key|1112619|text|在这种情况下，全局变量是有意义的。另一种可能是将值附加到DOM元素：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1112620|element.onmousedown+=+function()+{
++++//+'this'+should+point+to+the+element+being+mouse+downed
++++this.data+=+precalculate();+
};

element.onmouseup+=+function()+{
++++//+'this'+should+point+to+the+element+being+mouse+upped
++++var+data+=+this.data;
++++dosomething(data);
};|code-block|syntax|javascript|1112621|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|$]]

In this case a global variable would make sense. Another possibility is to attach the value to the DOM element:

<pre><code>element.onmousedown = function() {
 // 'this' should point to the element being mouse downed
 this.data = precalculate(); 
};

element.onmouseup = function() {
 // 'this' should point to the element being mouse upped
 var data = this.data;
 dosomething(data);
};
</code></pre>

blocks|key|4801940|text|你误解了“全局变量是邪恶的”。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4801941|事实上，实际发生的情况是，有人想成为“人群中的一部分”，因此告诉你一个全面的概括，而实际上他们应该说“只在适当的地方使用全局变量”。|4801942|它们在这里很合适，我的朋友。|4801943|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

You misunderstood "global variable is evil".

In fact, what really happened is that someone wanted to be "part of the crowd", and so told you a sweeping generalisation, when in fact they should have said "only use global variables where appropriate".

Well, they are appropriate here, my friend.

blocks|key|3015016|text|JQuery通过使用.data()函数实现了这一点：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3015017|http://api.jquery.com/jQuery.data/|offset|length|3015018|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|Y|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@$D|O|E|P|1|Q]]|A|$]]|$1|F|3|-4|5|6|7|R|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|C]]]]

JQuery makes this possible by using the .data() function:

<a href="http://api.jquery.com/jQuery.data/" rel="nofollow">http://api.jquery.com/jQuery.data/</a>

blocks|key|4801981|text|如果你不想/需要变量是全局的，只需限定它的作用域：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4801982|(function()+{
++++var+data;
++++element.onmousedown+=+function()+{
++++++++data+=+precalculate();
++++}

++++element.onmouseup+=+function()+{
++++++++dosomething(data);
++++}
})();|code-block|syntax|javascript|4801983|4801984|javascript+EDIT：澄清一下，在中创建新变量作用域的唯一方法是在函数中。|offset|length|style|BOLD|4801985|在函数内部使用var声明的任何变量对于外部作用域都是不可访问的。|CODE|4801986|在上面的代码中，我创建了一个IIFE+(立即调用的函数表达式)，它只是一个在创建后立即调用的函数，并且我将data变量(以及处理程序赋值)放在其中。|4801987|因为处理程序是在可以访问data变量的作用域中创建的，所以它们保留了对该变量的访问权限。|4801988|再举一个例子：|4801989|var+a+=+"a";+//+global+variable

(function()+{

++++var+b+=+"b";++//+new+variable+in+this+scope

++++(function()+{

++++++++var+c+=+"c";++//+new+variable+in+this+scope

++++++++//+in+this+function,+you+have+access+to+'a',+'b'+and+'c'

++++})();

++++//+in+this+function+you+have+access+to+'a'+and+'b'+variables,+but+not+'c'

})();

//+globally,+you+have+access+to+the+'a'+variable,+but+not+'b'+or+'c'|4801990|entityMap^0|0|0|0|M|K|0|0|W|7|3|0|0|22|1H|4|0|0|18|C|4|0|0|7|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|12|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|13|8|@$J|14|K|15|L|M]]|9|@]|A|$]]|$1|N|3|O|5|6|7|16|8|@$J|17|K|18|L|M]|$J|19|K|1A|L|P]]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1B|8|@$J|1C|K|1D|L|M]|$J|1E|K|1F|L|P]]|9|@]|A|$]]|$1|S|3|T|5|6|7|1G|8|@$J|1H|K|1I|L|M]|$J|1J|K|1K|L|P]]|9|@]|A|$]]|$1|U|3|V|5|6|7|1L|8|@$J|1M|K|1N|L|M]]|9|@]|A|$]]|$1|W|3|X|5|D|7|1O|8|@]|9|@]|A|$E|F]]|$1|Y|3|-4|5|6|7|1P|8|@]|9|@]|A|$]]]|Z|$]]

Just scope the variable if you don't want/need it to be global:

<pre><code>(function() {
 var data;
 element.onmousedown = function() {
 data = precalculate();
 }

 element.onmouseup = function() {
 dosomething(data);
 }
})();
</code></pre>

<hr>

EDIT: To clarify, the only way to create a new variable scope in javascript is in a function.

Any variable declared with <code>var</code> inside a function is inaccessible to the outer scope.

In the code above, I created an IIFE (immediately invoked function expression), which is simply a function that is invoked as soon as it is created, and I placed your <code>data</code> variable (along with the handler assignments) inside of it.

Because the handlers were created in a scope that has access to the <code>data</code> variable, they retain their access to that variable.

To give another example:

<pre><code>var a = "a"; // global variable

(function() {

 var b = "b"; // new variable in this scope

 (function() {

 var c = "c"; // new variable in this scope

 // in this function, you have access to 'a', 'b' and 'c'

 })();

 // in this function you have access to 'a' and 'b' variables, but not 'c'

})();

// globally, you have access to the 'a' variable, but not 'b' or 'c'
</code></pre>

blocks|key|4802005|text|您可以使用全局变量，只要您将它们保持在最低限度，例如，您可以将内容放在单个全局名称空间中：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4802006|App+=+{};

element.onmousedown+=+function()+{
+++App.data+=+"hello";
}

element.onmouseup+=+function()+{
+++console.log(App.data);
}|code-block|syntax|javascript|4802007|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|$]]

You can get away with using global variables as long as you keep them to a minimum, for example you can place stuff in a single global namespace:

<pre><code>App = {};

element.onmousedown = function() {
 App.data = "hello";
}

element.onmouseup = function() {
 console.log(App.data);
}
</code></pre>

blocks|key|1112712|text|另一种更通用的解决方案是使用一种称为memoization的技术来创建缓存其结果的函数。如果你搜索一下，就会发现有很多东西。下面的代码就是这样做的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1112713|Function.prototype.memoize+=+function()+{
++++var+fn+=+this;
++++this.memory+=+{};
++++return+function()+{
++++++++var+args+=+Array.prototype.slice.call(arguments);
++++++++return+fn.memory[args]+?+fn.memory[args]+:+fn.memory[args]+=+fn.apply(this,+arguments);
++++};
};|code-block|syntax|javascript|1112714|例如，你有一个名为exfunc的昂贵函数。|1112715|newFunc+=+exfunc.memoize();|1112716|上面的语句创建了一个名为newFunc的新函数，该函数缓存原始函数的结果，以便在第一次执行实际代码时，从本地缓存中检索所有后续调用。|1112717|这主要适用于返回值不依赖于全局状态的函数。|1112718|更多信息：http://osteele.com/archives/2006/04/javascript-memoization|offset|length|1112719|entityMap|0|LINK|mutability|MUTABLE|url|http://osteele.com/archives/2006/04/javascript-memoization^0|0|0|0|0|0|0|5|1M|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|12|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|14|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|15|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|16|8|@]|9|@$Q|17|R|18|1|19]]|A|$]]|$1|S|3|-4|5|6|7|1A|8|@]|9|@]|A|$]]]|T|$U|$5|V|W|X|A|$Y|Z]]]]

Another more general solution is to create functions that cache their results using a technique that is called memoization. There's plenty of stuff if you search. 
The following code does exactly that :

<pre><code>Function.prototype.memoize = function() {
 var fn = this;
 this.memory = {};
 return function() {
 var args = Array.prototype.slice.call(arguments);
 return fn.memory[args] ? fn.memory[args] : fn.memory[args] = fn.apply(this, arguments);
 };
};
</code></pre>

e.g. You have an expensive function called exfunc..

<pre><code>newFunc = exfunc.memoize();
</code></pre>

The above statement creates a new function called newFunc that caches the result of the original function so that the first time the actual code is being executed and all subsequent calls are retrieved from a local cache. 

This mostly works with functions whose return value does not depend on global state.

More info : 
<a href="http://osteele.com/archives/2006/04/javascript-memoization" rel="nofollow">http://osteele.com/archives/2006/04/javascript-memoization</a>

What I want to do is to sending data between two handlers.

<pre><code>element.onmousedown = function() {
 data = precalculate();
}

element.onmouseup = function() {
 dosomething(data);
}
</code></pre>

if the <code>data</code> is a global variable it works. People says global variable is evil. But I don't know how to do without it.

or I misunderstood "global variable"?

How to cache/precalculate something(without global variable)?

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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我想要做的是在两个处理程序之间发送数据。element.onmousedown = function() {    data = precalculate();}element.onmouseup = function() {    dosomething(data);}如果data是一个全局变量，那么它就可以工作。人...

问如何缓存/预计算一些东西(没有全局变量)？
EN

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问如何缓存/预计算一些东西(没有全局变量)？EN