blocks|key|1187215|text|如果这是您要使用此变量的唯一应用程序，那么Felix's+approach是非常好的选择。但是，如果您正在编写jQuery插件，请考虑“命名空间”(稍后将详细介绍引号...)jQuery对象下需要的变量和函数。例如，我目前正在开发一个名为miniMenu的jQuery弹出菜单。因此，我在jQuery下定义了一个“名称空间”miniMenu，并将所有内容都放在那里。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1187216|我在讨论JavaScript名称空间时使用引号的原因是，它们并不是通常意义上的名称空间。相反，我只需使用一个JavaScript对象，并将我所有的函数和变量作为该对象的属性。|1187217|此外，为了方便起见，我通常会将插件名称空间划分为i名称空间，用于只在插件内部使用的内容，以便对插件用户隐藏它。|1187218|它是这样工作的：|1187219|//+An+object+to+define+utility+functions+and+global+variables+on:
$.miniMenu+=+new+Object();
//+An+object+to+define+internal+stuff+for+the+plugin:
$.miniMenu.i+=+new+Object();|code-block|syntax|javascript|1187220|现在，当我需要全局保存某些内容时，我可以只执行$.miniMenu.i.globalVar+=+3或$.miniMenu.i.parseSomeStuff+=+function(...)+{...}，并且我仍然将其放在全局名称空间之外。|1187221|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/3352020/how-to-declare-a-global-variable-in-javascript/3352033#3352033^0|4I|8|L|G|0|0|0|O|1|0|0|0|N|Q|1E|1D|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@$9|13|A|14|1|15]]|E|$]]|$1|F|3|G|5|6|7|16|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|1A|8|@]|D|@]|E|$]]|$1|L|3|M|5|N|7|1B|8|@]|D|@]|E|$O|P]]|$1|Q|3|R|5|6|7|1C|8|@$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]]|D|@]|E|$]]|$1|S|3|-4|5|6|7|1H|8|@]|D|@]|E|$]]]|T|$U|$5|V|W|X|E|$Y|Z]]]]

If this is the only application where you're going to use this variable, <a href="https://stackoverflow.com/questions/3352020/how-to-declare-a-global-variable-in-javascript/3352033#3352033">Felix's approach</a> is excellent. However, if you're writing a jQuery plugin, consider &quot;namespacing&quot; (details on the quotes later...) variables and functions needed under the jQuery object. For example, I'm currently working on a jQuery popup menu that I've called miniMenu. Thus, I've defined a &quot;namespace&quot; <code>miniMenu</code> under jQuery, and I place everything there.
The reason I use quotes when I talk about JavaScript namespaces is that they aren't really namespaces in the normal sense. Instead, I just use a JavaScript object and place all my functions and variables as properties of this object.
Also, for convenience, I usually sub-space the plugin namespace with an <code>i</code> namespace for stuff that should only be used internally within the plugin, so as to hide it from users of the plugin.
This is how it works:
<pre><code>// An object to define utility functions and global variables on:
$.miniMenu = new Object();
// An object to define internal stuff for the plugin:
$.miniMenu.i = new Object();
</code></pre>
Now I can just do <code>$.miniMenu.i.globalVar = 3</code> or <code>$.miniMenu.i.parseSomeStuff = function(...) {...}</code> whenever I need to save something globally, and I still keep it out of the global namespace.

blocks|key|1187293|text|下面是一个全局变量的基本示例，您的其余函数都可以访问它。这是一个活生生的例子：http://jsfiddle.net/fxCE9/|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1187294|var+myVariable+=+'Hello';
alert('value:+'+%2B+myVariable);
myFunction1();
alert('value:+'+%2B+myVariable);
myFunction2();
alert('value:+'+%2B+myVariable);


function+myFunction1()+{
++++myVariable+=+'Hello+1';
}

function+myFunction2()+{
++++myVariable+=+'Hello+2';
}|code-block|syntax|javascript|1187295|如果您在jQuery+ready()函数中执行此操作，请确保您的变量与其他函数一起位于ready()函数中。|1187296|entityMap|0|LINK|mutability|MUTABLE|url|http://jsfiddle.net/fxCE9/^0|13|Q|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@$A|T|B|U|1|V]]|C|$]]|$1|D|3|E|5|F|7|W|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|X|8|@]|9|@]|C|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]]]

Here is a basic example of a global variable that the rest of your functions can access. Here is a live example for you: <a href="http://jsfiddle.net/fxCE9/" rel="nofollow noreferrer">http://jsfiddle.net/fxCE9/</a>
<pre><code>var myVariable = 'Hello';
alert('value: ' + myVariable);
myFunction1();
alert('value: ' + myVariable);
myFunction2();
alert('value: ' + myVariable);


function myFunction1() {
 myVariable = 'Hello 1';
}

function myFunction2() {
 myVariable = 'Hello 2';
}
</code></pre>
If you are doing this within a jQuery ready() function then make sure your variable is inside the ready() function along with your other functions.

blocks|key|1187353|text|在函数外部声明变量|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1187354|function+dosomething(){
++var+i+=+0;+//+Can+only+be+used+inside+function
}

var+i+=+'';
function+dosomething(){
++i+=+0;+//+Can+be+used+inside+and+outside+the+function
}|code-block|syntax|javascript|1187355|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|$]]

Declare the variable outside of functions
<pre><code>function dosomething(){
 var i = 0; // Can only be used inside function
}

var i = '';
function dosomething(){
 i = 0; // Can be used inside and outside the function
}
</code></pre>

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