blocks|key|942348|text|在jQuery的作用域之外声明它|type|unstyled|depth|inlineStyleRanges|entityRanges|data|942349|var+option+=+'';

$(document).ready(function()+{
++++$("[name=select_option_selected]").change(function()+{+
++++++++option+=+$(this).val();
++++++++alert(option);+//+Example:+Foo++
++++});

++++alert(option);+//This+will+never+be+"Foo"+since+option+isn't+set+until+that+select+list+changes
});|code-block|syntax|javascript|942350|如果您想将其初始化为当前选定的值，请尝试执行以下操作：|942351|var+option+=+"";
var+$select_option_selected+=+null;

$(function()+{++++++++
++++$select_option_selected+=+$("[name='select_option_selected']")
++++$select_option_selected.change(function()+{+
++++++++option+=+$(this).val();
++++});++++
++++option+=+$select_option_selected.val();
});|942352|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|$]]

Declare it outside the scope of your jQuery onready

<pre><code>var option = '';

$(document).ready(function() {
 $("[name=select_option_selected]").change(function() { 
 option = $(this).val();
 alert(option); // Example: Foo 
 });

 alert(option); //This will never be "Foo" since option isn't set until that select list changes
});
</code></pre>

if you want to initialize this to the current selected value try this:

<pre><code>var option = "";
var $select_option_selected = null;

$(function() { 
 $select_option_selected = $("[name='select_option_selected']")
 $select_option_selected.change(function() { 
 option = $(this).val();
 }); 
 option = $select_option_selected.val();
});
</code></pre>

blocks|key|726278|text|你确定要这样做吗？通常要避免使用全局变量。在浏览器中，window是全局对象，因此如果执行window.option+=+...，则option将全局可用。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|726279|我强烈建议将全局变量命名为比"option“更独特的名称，以避免破坏现有的内容。|726280|另一种选择，我也不推荐:不使用var|726281|myvariable+=+'foo';|code-block|syntax|javascript|726282|如果myvariable以前从未被删除过，那么它将被声明为window上的一个属性，从而使其成为全局的。然而，这通常被认为是(非常)糟糕的做法。|726283|entityMap^0|R|6|19|J|1U|6|0|0|F|3|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Z|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|J|3|K|5|L|7|13|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|14|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|15|8|@]|D|@]|E|$]]]|R|$]]

Are you sure you want to? global variables are generally to be avoided. In the browser, <code>window</code> is the global object, so if you do <code>window.option = ...</code>, then <code>option</code> will be available globally. 

I highly recommend naming a global variable something more unique than "option", to avoid clobbering existing stuff. 

Another option, which I also don't recommend: leave off <code>var</code> 

<pre><code>myvariable = 'foo';
</code></pre>

If myvariable has never been delcared before, it will be declared as a property on window, making it global. This is generally considered to be (very) bad practice however.

blocks|key|726292|text|$(document).ready(function()+{
++++var+option+=+'';

++++$("[name=select_option_selected]").change(function()+{+
++++++++option+=+$(this).val();+//no+declaration+of+new+variable,+JavaScript+goes+to+what+encloses+the+function
++++++++alert(option);+//+Example:+Foo++
++++});

++++alert(option);+//+Need+it+to+alert+Foo+from+the+above+change+function++++
});|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|726293|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>$(document).ready(function() {
 var option = '';

 $("[name=select_option_selected]").change(function() { 
 option = $(this).val(); //no declaration of new variable, JavaScript goes to what encloses the function
 alert(option); // Example: Foo 
 });

 alert(option); // Need it to alert Foo from the above change function 
});
</code></pre>

blocks|key|726333|text|可以使用window.前缀从函数范围内访问全局变量|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|726334|window.option+=+...;|code-block|syntax|javascript|726335|entityMap^0|4|7|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 use the <code>window.</code> prefix to access a global variable from within the scope of a function 

<pre><code>window.option = ...;
</code></pre>

blocks|key|726375|text|只需声明一个全局对象|type|unstyled|depth|inlineStyleRanges|entityRanges|data|726376|var+obj={};
function+my_function()
{
+obj['newVariable']+=+'someValue';
}|code-block|syntax|javascript|726377|这样我就实现了全局变量。|726378|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

just declare a global object 

<pre><code>var obj={};
function my_function()
{
 obj['newVariable'] = 'someValue';
}
</code></pre>

in this way i achieved global variable.

blocks|key|726425|text|http://jsfiddle.net/Kba5u/|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|726426|var+foo+=+'bar';

function+changeFooToBaz(){
+++foo+=+'baz';
}

//+changeFooToBaz();
console.log(foo);+#=>+'bar'|code-block|syntax|javascript|726427|现在，取消对changeFooToBaz调用的注释|style|CODE|726428|var+foo+=+'bar';

function+changeFooToBaz(){
+++foo+=+'baz';
}

changeFooToBaz();
console.log(foo);+#=>+'baz'|726429|changeFooToBaz确实更改了foo的内容，该变量是在比函数更高的作用域中声明的。|726430|entityMap|0|LINK|mutability|MUTABLE|url^0|0|Q|0|0|0|6|E|0|0|0|E|J|3|0^^$0|@$1|2|3|4|5|6|7|X|8|@]|9|@$A|Y|B|Z|1|10]]|C|$]]|$1|D|3|E|5|F|7|11|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|12|8|@$A|13|B|14|K|L]]|9|@]|C|$]]|$1|M|3|N|5|F|7|15|8|@]|9|@]|C|$G|H]]|$1|O|3|P|5|6|7|16|8|@$A|17|B|18|K|L]|$A|19|B|1A|K|L]]|9|@]|C|$]]|$1|Q|3|-4|5|6|7|1B|8|@]|9|@]|C|$]]]|R|$S|$5|T|U|V|C|$W|4]]]]

<a href="http://jsfiddle.net/Kba5u/" rel="nofollow">http://jsfiddle.net/Kba5u/</a>

<pre><code>var foo = 'bar';

function changeFooToBaz(){
 foo = 'baz';
}

// changeFooToBaz();
console.log(foo); #=&gt; 'bar'
</code></pre>

Now, uncomment the call to <code>changeFooToBaz</code>:

<pre><code>var foo = 'bar';

function changeFooToBaz(){
 foo = 'baz';
}

changeFooToBaz();
console.log(foo); #=&gt; 'baz'
</code></pre>

<code>changeFooToBaz</code> has indeed changed the contents of <code>foo</code>, a variable that was declared at a higher scope than the function.

How can I set a Global Variable from within a function?

<pre><code>$(document).ready(function() {
 var option = '';

 $("[name=select_option_selected]").change(function() { 
 var option = $(this).val();
 alert(option); // Example: Foo 
 });

 alert(option); // Need it to alert Foo from the above change function 
});
</code></pre>

How can I set a Global Variable from within a function

jQuery

如何从函数中设置全局变量？$(document).ready(function() {    var option = '';    $("[name=select_option_selected]").change(function() {         var option = $(this).val();   ...

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