blocks|key|936330|text|function+js_to_as(+str+){
+++++if+(me+&&+me.onChange)
+++++++++me.onChange(str);
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|936331|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>function js_to_as( str ){
 if (me &amp;&amp; me.onChange)
 me.onChange(str);
}
</code></pre>

blocks|key|810385|text|试着做这样的事情：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|810386|if+(typeof+me.onChange+!==+"undefined")+{+
++++//+safe+to+use+the+function
}|code-block|syntax|javascript|810387|或者更好一些(根据UpTheCreek的投票结果)|810388|if+(typeof+me.onChange+===+"function")+{+
++++//+safe+to+use+the+function
}|810389|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|$]]

Try something like this:

<pre><code>if (typeof me.onChange !== "undefined") { 
 // safe to use the function
}
</code></pre>

or better yet (as per UpTheCreek upvoted comment)

<pre><code>if (typeof me.onChange === "function") { 
 // safe to use the function
}
</code></pre>

blocks|key|2336489|text|没有任何条件|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2336490|me.onChange=function(){};

function+getID(+swfID+){
+++++if(navigator.appName.indexOf("Microsoft")+!=+-1){
++++++++++me+=+window[swfID];
+++++}else{
++++++++++me+=+document[swfID];
+++++}
}

function+js_to_as(+str+){
+++++me.onChange(str);
}|code-block|syntax|javascript|2336491|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|$]]

With no conditions

<pre><code>me.onChange=function(){};

function getID( swfID ){
 if(navigator.appName.indexOf("Microsoft") != -1){
 me = window[swfID];
 }else{
 me = document[swfID];
 }
}

function js_to_as( str ){
 me.onChange(str);
}
</code></pre>

blocks|key|936378|text|我怀疑me没有得到正确的负载分配。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|936379|将get_ID调用移动到onclick事件中应该会处理它。|936380|显然，正如前面提到的，您可以进一步设置陷阱：|936381|function+js_to_as(+str)+{
++var+me+=+get_ID('jsExample');
++if+(me+&&+me.onChange)+{
++++me.onChange(str);
++}
}|code-block|syntax|javascript|936382|entityMap^0|3|2|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|U|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|V|8|@]|D|@]|E|$M|N]]|$1|O|3|-4|5|6|7|W|8|@]|D|@]|E|$]]]|P|$]]

I would suspect that <code>me</code> is not getting correctly assigned onload.

Moving the get_ID call into the onclick event should take care of it.

Obviously you can further trap as previously mentioned:

<pre><code>function js_to_as( str) {
 var me = get_ID('jsExample');
 if (me &amp;&amp; me.onChange) {
 me.onChange(str);
 }
}
</code></pre>

blocks|key|810466|text|我将更进一步确保该属性确实是一个函数|type|unstyled|depth|inlineStyleRanges|entityRanges|data|810467|function+js_to_as(+str+){
+++++if+(me+&&+me.onChange+&&+typeof+me.onChange+===+'function')+{
+++++++++me.onChange(str);
+++++}
}|code-block|syntax|javascript|810468|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'll go 1 step further to make sure the property is indeed a function

<pre><code>function js_to_as( str ){
 if (me &amp;&amp; me.onChange &amp;&amp; typeof me.onChange === 'function') {
 me.onChange(str);
 }
}
</code></pre>

blocks|key|936906|text|如果您正在使用eval将字符串转换为函数，并且要检查此method方法是否存在，则需要使用类型的，并在中使用函数字符串|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|936907|var+functionString+=+"nonexsitantFunction"
eval("typeof+"+%2B+functionString)+//+returns+"undefined"+or+"function"|code-block|syntax|javascript|936908|不要逆转这种情况，并尝试在+reverse+上使用类型。如果您这样做，将抛出一个ReferenceError：|936909|var+functionString+=+"nonexsitantFunction"
typeof(eval(functionString))+//+returns+ReferenceError:+[function]+is+not+defined|936910|entityMap^0|19|3|0|0|D|9|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|P|$]]

If you're using eval to convert a string to function, and you want to check if this eval'd method exists, you'll want to use typeof and your function string inside an eval:

<pre><code>var functionString = "nonexsitantFunction"
eval("typeof " + functionString) // returns "undefined" or "function"
</code></pre>

Don't reverse this and try a typeof on eval. If you do a ReferenceError will be thrown:

<pre><code>var functionString = "nonexsitantFunction"
typeof(eval(functionString)) // returns ReferenceError: [function] is not defined
</code></pre>

blocks|key|936918|text|我有这个问题。如果if+(obj+&&+typeof+obj+===+'function')+{+...+}碰巧是undefined，那么obj会一直抛出一个引用错误，所以最后我做了以下操作：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|936919|if+(typeof+obj+!==+'undefined'+&&+typeof+obj+===+'function')+{+...+}|code-block|syntax|javascript|936920|然而，一位同事向我指出，检查它是否是!==+'undefined'，然后检查===+'function'是否是多余的，因此：|936921|更简单：|BOLD|936922|if+(typeof+obj+===+'function')+{+...+}|936923|干净得多，效果也很好。|936924|entityMap^0|9|19|1L|9|1X|3|0|0|I|F|12|E|0|0|4|0|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@$9|W|A|X|B|C]|$9|Y|A|Z|B|C]|$9|10|A|11|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|12|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|13|8|@$9|14|A|15|B|C]|$9|16|A|17|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|18|8|@$9|19|A|1A|B|O]]|D|@]|E|$]]|$1|P|3|Q|5|H|7|1B|8|@]|D|@]|E|$I|J]]|$1|R|3|S|5|6|7|1C|8|@]|D|@]|E|$]]|$1|T|3|-4|5|6|7|1D|8|@]|D|@]|E|$]]]|U|$]]

I had this problem. <code>if (obj &amp;&amp; typeof obj === 'function') { ... }</code> kept throwing a reference error if <code>obj</code> happened to be <code>undefined</code>, so in the end I did the following:
<pre><code>if (typeof obj !== 'undefined' &amp;&amp; typeof obj === 'function') { ... }
</code></pre>
However, a colleague pointed out to me that checking if it's <code>!== 'undefined'</code> and then <code>=== 'function'</code> is redundant, thus:
Simpler:
<pre><code>if (typeof obj === 'function') { ... }
</code></pre>
Much cleaner and works great.

blocks|key|2336767|text|尝试typeof+--寻找'undefined'说它不存在，函数的'function'。此代码的JSFiddle|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2336768|function+thisishere()+{
++++return+false;
}
alert("thisishere()+is+a+"+%2B+typeof+thisishere);
alert("thisisnthere()+is+"+%2B+typeof+thisisnthere);|code-block|syntax|javascript|2336769|或作为一种情况：|2336770|if+(typeof+thisishere+===+'function')+{
++++//+function+exists
}|2336771|或在单行上具有返回值：|2336772|var+exists+=+(typeof+thisishere+===+'function')+?+"Value+if+true"+:+"Value+if+false";
var+exists+=+(typeof+thisishere+===+'function')+//+Returns+true+or+false|2336773|entityMap|0|LINK|mutability|MUTABLE|url|http://jsfiddle.net/3rjAL/^0|2|6|D|B|X|A|18|C|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@$9|17|A|18|1|19]]|E|$]]|$1|F|3|G|5|H|7|1A|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1B|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|1C|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1D|8|@]|D|@]|E|$]]|$1|Q|3|R|5|H|7|1E|8|@]|D|@]|E|$I|J]]|$1|S|3|-4|5|6|7|1F|8|@]|D|@]|E|$]]]|T|$U|$5|V|W|X|E|$Y|Z]]]]

Try <code>typeof</code> -- Look for <code>'undefined'</code> to say it doesn't exist, <code>'function'</code> for a function. <a href="http://jsfiddle.net/3rjAL/" rel="noreferrer">JSFiddle for this code</a>

<pre><code>function thisishere() {
 return false;
}
alert("thisishere() is a " + typeof thisishere);
alert("thisisnthere() is " + typeof thisisnthere);
</code></pre>

Or as an if:

<pre><code>if (typeof thisishere === 'function') {
 // function exists
}
</code></pre>

Or with a return value, on a single line:

<pre><code>var exists = (typeof thisishere === 'function') ? "Value if true" : "Value if false";
var exists = (typeof thisishere === 'function') // Returns true or false
</code></pre>

blocks|key|2336790|text|我总是这样检查：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2336791|if(!myFunction){return+false;}|code-block|syntax|javascript|2336792|只需将其放在任何使用此函数的代码之前即可。|2336793|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|$]]

I always check like this:

<pre><code>if(!myFunction){return false;}
</code></pre>

just place it before any code that uses this function

blocks|key|936994|text|不如：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|936995|if('functionName'+in+Obj){
++++//code
}|code-block|syntax|javascript|936996|例如：|936997|var+color1+=+new+String("green");
"length"+in+color1+//+returns+true
"indexOf"+in+color1+//+returns+true
"blablabla"+in+color1+//+returns+false|936998|或者说你的案子：|936999|if('onChange'+in+me){
++++//code
}|937000|见MDN文档。|offset|length|937001|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/in^0|0|0|0|0|0|0|1|5|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]]|$1|K|3|L|5|6|7|14|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|15|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|16|8|@]|9|@$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]]]]

How about:

<pre><code>if('functionName' in Obj){
 //code
}
</code></pre>

e.g. 

<pre><code>var color1 = new String("green");
"length" in color1 // returns true
"indexOf" in color1 // returns true
"blablabla" in color1 // returns false
</code></pre>

or as for your case:

<pre><code>if('onChange' in me){
 //code
}
</code></pre>

See <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/in" rel="noreferrer">MDN docs</a>.

blocks|key|937003|text|//Simple+function+that+will+tell+if+the+function+is+defined+or+not
function+is_function(func)+{
++++return+typeof+window[func]+!==+'undefined'+&&+$.isFunction(window[func]);
}

//usage

if+(is_function("myFunction")+{
++++++++alert("myFunction+defined");
++++}+else+{
++++++++alert("myFunction+not+defined");
++++}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|937004|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>//Simple function that will tell if the function is defined or not
function is_function(func) {
 return typeof window[func] !== 'undefined' &amp;&amp; $.isFunction(window[func]);
}

//usage

if (is_function("myFunction") {
 alert("myFunction defined");
 } else {
 alert("myFunction not defined");
 }
</code></pre>

blocks|key|810694|text|我喜欢使用这种方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|810695|function+isFunction(functionToCheck)+{
++var+getType+=+{};
++return+functionToCheck+&&+getType.toString.call(functionToCheck)+===+'[object+Function]';
}|code-block|syntax|javascript|810696|用法：|810697|if+(+isFunction(me.onChange)+)+{
++++me.onChange(str);+//+call+the+function+with+params
}|810698|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|$]]

I like using this method:

<pre><code>function isFunction(functionToCheck) {
 var getType = {};
 return functionToCheck &amp;&amp; getType.toString.call(functionToCheck) === '[object Function]';
}
</code></pre>

Usage:

<pre><code>if ( isFunction(me.onChange) ) {
 me.onChange(str); // call the function with params
}
</code></pre>

blocks|key|810704|text|未见此提示:+me.onChange+&+me.onChange(str)；|type|unstyled|depth|inlineStyleRanges|entityRanges|data|810705|基本上，如果me.onChange是未定义的(如果它还没有启动的话就会是这样)，那么它就不会执行后一部分。如果me.onChange是一个函数，它将执行me.onChange(str)。|810706|你甚至可以更进一步：|810707|me+&&+me.onChange+&&+me.onChange(str);|code-block|syntax|javascript|810708|万一我也是异步的。|810709|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Q|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|R|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Didn't see this suggested:
 me.onChange &amp;&amp; me.onChange(str);

Basically if me.onChange is undefined (which it will be if it hasn't been initiated) then it won't execute the latter part. If me.onChange is a function, it will execute me.onChange(str).

You can even go further and do:

<pre><code>me &amp;&amp; me.onChange &amp;&amp; me.onChange(str);
</code></pre>

in case me is async as well.

blocks|key|936538|text|Underscore.js库在isFunction方法中将其定义为如下(注释表明这可能满足某些浏览器错误)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|936539|typeof+obj+==+'function'+%7C%7C+false|code-block|syntax|javascript|936540|http://underscorejs.org/docs/underscore.html#section-143|offset|length|936541|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|0|1K|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|T|8|@]|9|@$I|U|J|V|1|W]]|A|$]]|$1|K|3|-4|5|6|7|X|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|H]]]]

The Underscore.js library defines it in the isFunction method as this (which comments suggest may cater for some browser bugs)

<pre><code>typeof obj == 'function' || false
</code></pre>

<a href="http://underscorejs.org/docs/underscore.html#section-143" rel="nofollow">http://underscorejs.org/docs/underscore.html#section-143</a>

blocks|key|937079|text|在这种情况下，函数的名称根据添加到函数名称中的变量(在本例中为var+'x‘)而变化。这样做是可行的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|937080|if+(+typeof+window['afunction_'%2Bx]+===+'function'+)+{+window['afunction_'%2Bx]();+}+|code-block|syntax|javascript|937081|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 had the case where the name of the function varied according to a variable (var 'x' in this case) added to the functions name. This works:

<pre><code>if ( typeof window['afunction_'+x] === 'function' ) { window['afunction_'+x](); } 
</code></pre>

blocks|key|936547|text|这个简单的jQuery代码应该可以做到这一点：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|936548|if+(jQuery.isFunction(functionName))+{
++++functionName();
}|code-block|syntax|javascript|936549|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|$]]

This simple jQuery code should do the trick:

<pre><code>if (jQuery.isFunction(functionName)) {
 functionName();
}
</code></pre>

blocks|key|810763|text|如果您正在检查一个是jQuery插件的函数，则需要使用$.fn.myfunction|type|unstyled|depth|inlineStyleRanges|entityRanges|data|810764|if+(typeof+$.fn.mask+===+'function')+{
++++$('.zip').mask('00000');
}|code-block|syntax|javascript|810765|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|$]]

If you're checking for a function that is a jQuery plugin, you need to use $.fn.myfunction

<pre><code>if (typeof $.fn.mask === 'function') {
 $('.zip').mask('00000');
}
</code></pre>

blocks|key|2336917|text|我尝试了接受的答案，但是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2336918|console.log(typeof+me.onChange);|code-block|syntax|javascript|2336919|返回“未定义”。我注意到规范描述了一个名为'onchange‘的事件，而不是'onChange’(请注意camelCase)。|2336920|对我来说，改变原来接受的答案对我是有效的：|2336921|if+(typeof+me.onchange+===+"function")+{+
++//+safe+to+use+the+function
}|2336922|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I have tried the accepted answer; however:

<pre><code>console.log(typeof me.onChange);
</code></pre>

returns 'undefined'.
I've noticed that the specification states an event called 'onchange' instead of 'onChange' (notice the camelCase).

Changing the original accepted answer to the following worked for me:

<pre><code>if (typeof me.onchange === "function") { 
 // safe to use the function
}
</code></pre>

blocks|key|2336926|text|++++function+sum(nb1,nb2){

+++++++return+nb1%2Bnb2;
++++}

++++try{

++++++if(sum()+!=+undefined){/*test+if+the+function+is+defined+before+call+it*/

++++++++sum(3,5);+++++++++++++++/*once+the+function+is+exist+you+can+call+it+*/

++++++}

++++}catch(e){

++++++console.log("function+not+defined");/*the+function+is+not+defined+or+does+not+exists*/
++++}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|2336927|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> function sum(nb1,nb2){

 return nb1+nb2;
 }

 try{

 if(sum() != undefined){/*test if the function is defined before call it*/

 sum(3,5); /*once the function is exist you can call it */

 }

 }catch(e){

 console.log("function not defined");/*the function is not defined or does not exists*/
 }
</code></pre>

blocks|key|810848|text|然后是这个..。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|810849|(+document.exitPointerLock+%7C%7C+Function+)();|code-block|syntax|javascript|810850|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|$]]

And then there is this...

<pre><code>( document.exitPointerLock || Function )();
</code></pre>

blocks|key|937155|text|这里是一个简单的工作解决方案，用于检查是否存在一个函数和，通过另一个函数动态地触发该函数；|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|937156|触发函数|937157|function+runDynamicFunction(functionname){+

++++if+(typeof+window[functionname]+==+"function")+{+//check+availability

++++++++window[functionname]("this+is+from+the+function+it");+//+run+function+and+pass+a+parameter+to+it
++++}
}|code-block|syntax|javascript|937158|现在您可以动态地生成函数，例如使用php|937159|function+runThis_func(my_Parameter){

++++alert(my_Parameter+%2B"+triggerd");
}|937160|现在，您可以使用动态生成的事件调用该函数。|937161|<?php

$name_frm_somware+="runThis_func";

echo+"<input+type='button'+value='Button'+onclick='runDynamicFunction(\"".$name_frm_somware."\");'>";

?>|937162|您需要的确切HTML代码是|937163|<input+type="button"+value="Button"+onclick="runDynamicFunction('runThis_func');">|937164|entityMap^0|J|8|S|H|0|0|4|0|0|0|K|0|0|0|L|0|0|0|D|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|15|8|@$9|16|A|17|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|18|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|19|8|@$9|1A|A|1B|B|C]]|D|@]|E|$]]|$1|O|3|P|5|J|7|1C|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|1D|8|@$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|S|3|T|5|J|7|1G|8|@]|D|@]|E|$K|L]]|$1|U|3|V|5|6|7|1H|8|@$9|1I|A|1J|B|C]]|D|@]|E|$]]|$1|W|3|X|5|J|7|1K|8|@]|D|@]|E|$K|L]]|$1|Y|3|-4|5|6|7|1L|8|@]|D|@]|E|$]]]|Z|$]]

Here is a working and simple solution for checking existence of a function and triggering that function dynamically by another function;

Trigger function

<pre><code>function runDynamicFunction(functionname){ 

 if (typeof window[functionname] == "function") { //check availability

 window[functionname]("this is from the function it"); // run function and pass a parameter to it
 }
}
</code></pre>

and you can now generate the function dynamically maybe using php like this

<pre><code>function runThis_func(my_Parameter){

 alert(my_Parameter +" triggerd");
}
</code></pre>

now you can call the function using dynamically generated event 

<pre><code>&lt;?php

$name_frm_somware ="runThis_func";

echo "&lt;input type='button' value='Button' onclick='runDynamicFunction(\"".$name_frm_somware."\");'&gt;";

?&gt;
</code></pre>

the exact HTML code you need is

<pre><code>&lt;input type="button" value="Button" onclick="runDynamicFunction('runThis_func');"&gt;
</code></pre>

blocks|key|810875|text|试试这个：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|810876|Window.function_exists=function(function_name,scope){
//Setting+default+scope+of+none+is+provided
If(typeof+scope+===+'undefined')+scope=window;
//Checking+if+function+name+is+defined
If+(typeof+function_name+===+'undefined')+throw+new+
Error('You+have+to+provide+an+valid+function+name!');
//The+type+container
var+fn=+(typeof+scope[function_name]);
//Function+type
If(fn+===+'function')+return+true;
//Function+object+type
if(fn.indexOf('function')!==+false)+return+true;+
return+false;
}|code-block|syntax|javascript|810877|请注意，我用手机写的这篇文章可能包含一些大写问题和/或其他需要修改的地方，比如函数名称|810878|如果您希望像PHP这样的函数检查var是否已设置：|810879|Window.isset=function+(variable_con){
If(typeof+variable_con+!==+'undefined')+return+true;
return+false;
}|810880|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Try this one:

<pre><code>Window.function_exists=function(function_name,scope){
//Setting default scope of none is provided
If(typeof scope === 'undefined') scope=window;
//Checking if function name is defined
If (typeof function_name === 'undefined') throw new 
Error('You have to provide an valid function name!');
//The type container
var fn= (typeof scope[function_name]);
//Function type
If(fn === 'function') return true;
//Function object type
if(fn.indexOf('function')!== false) return true; 
return false;
}
</code></pre>

Be aware that I've write this with my cellphone
Might contain some uppercase issues and/or other corrections needed like for example functions name

If you want a function like PHP to check if the var is set:

<pre><code>Window.isset=function (variable_con){
If(typeof variable_con !== 'undefined') return true;
return false;
}
</code></pre>

blocks|key|810894|text|为了说明前面的答案，这里有一个快速的JSFiddle片段：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|810895|​|810896|function+test+()+{
console.log()

}

console.log(typeof+test)+//+>>+"function"

//+implicit+test,+in+javascript+if+an+entity+exist+it+returns+implcitly+true+unless+the+element+value+is+false+as+:
//+var+test+=+false
if(test){+console.log(true)}
else{console.log(false)}

//+test+by+the+typeof+method
if(+typeof+test+===+"function"){+console.log(true)}
else{console.log(false)}


//+confirm+that+the+test+is+effective+:+
//+-+entity+with+false+value
var+test2+=+false
if(test2){+console.log(true)}
else{console.log(false)}

//+confirm+that+the+test+is+effective+:
//+-+typeof+entity
if(+typeof+test+==="foo"){+console.log(true)}
else{console.log(false)}

/*+Expected+:
function
true+
true+
false
false
*/|code-block|syntax|javascript|810897|810898|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|N|8|@]|9|@]|A|$G|H]]|$1|I|3|C|5|6|7|O|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|P|8|@]|9|@]|A|$]]]|K|$]]

To illustrate the preceding answers, here a quick JSFiddle snippet : 

<div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>function test () {
console.log()

}

console.log(typeof test) // &gt;&gt; "function"

// implicit test, in javascript if an entity exist it returns implcitly true unless the element value is false as :
// var test = false
if(test){ console.log(true)}
else{console.log(false)}

// test by the typeof method
if( typeof test === "function"){ console.log(true)}
else{console.log(false)}


// confirm that the test is effective : 
// - entity with false value
var test2 = false
if(test2){ console.log(true)}
else{console.log(false)}

// confirm that the test is effective :
// - typeof entity
if( typeof test ==="foo"){ console.log(true)}
else{console.log(false)}

/* Expected :
function
true 
true 
false
false
*/</code></pre>
</div>
</div>

blocks|key|2337035|text|对我来说，最简单的方法是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2337036|function+func_exists(fname)
{
++return+(typeof+window[fname]+===+'function');
}|code-block|syntax|javascript|2337037|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 me the easiest way :

<pre><code>function func_exists(fname)
{
 return (typeof window[fname] === 'function');
}
</code></pre>

blocks|key|937200|text|function+function_exists(function_name)
{
++++return+eval('typeof+'+%2B+function_name)+===+'function';
}
alert(function_exists('test'));
alert(function_exists('function_exists'));|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|937201|或|unstyled|937202|function+function_exists(func_name)+{
++//++discuss+at:+http://phpjs.org/functions/function_exists/
++//+original+by:+Kevin+van+Zonneveld+(http://kevin.vanzonneveld.net)
++//+improved+by:+Steve+Clay
++//+improved+by:+Legaev+Andrey
++//+improved+by:+Brett+Zamir+(http://brett-zamir.me)
++//+++example+1:+function_exists('isFinite');
++//+++returns+1:+true

++if+(typeof+func_name+===+'string')+{
++++func_name+=+this.window[func_name];
++}
++return+typeof+func_name+===+'function';
}|937203|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|L|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|I|3|-4|5|F|7|N|8|@]|9|@]|A|$]]]|J|$]]

<pre><code>function function_exists(function_name)
{
 return eval('typeof ' + function_name) === 'function';
}
alert(function_exists('test'));
alert(function_exists('function_exists'));
</code></pre>

OR

<pre><code>function function_exists(func_name) {
 // discuss at: http://phpjs.org/functions/function_exists/
 // original by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
 // improved by: Steve Clay
 // improved by: Legaev Andrey
 // improved by: Brett Zamir (http://brett-zamir.me)
 // example 1: function_exists('isFinite');
 // returns 1: true

 if (typeof func_name === 'string') {
 func_name = this.window[func_name];
 }
 return typeof func_name === 'function';
}
</code></pre>

blocks|key|2337042|text|加双感叹号，即!！在要检查的函数名称之前。如果它存在，它将返回true。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2337043|function+abc(){
}
!!window.abc;+//+return+true
!!window.abcd;+//+return+false|code-block|syntax|javascript|2337044|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|$]]

Put double exclamation mark i.e !! before the function name that you want to check. If it exists, it will return true.

<pre><code>function abc(){
}
!!window.abc; // return true
!!window.abcd; // return false
</code></pre>

blocks|key|2337061|text|我也一直在寻找一个优雅的解决这个问题的方法。经过多次思考，我发现这种方法是最好的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2337062|const+func+=++me.onChange+%7C%7C+(str+=>+{});+func(str)；|offset|length|style|CODE|2337063|entityMap^0|0|0|1F|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@$D|L|E|M|F|G]]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

I have also been looking for an elegant solution to this problem. After much reflection, I found this approach best.

<code>const func = me.onChange || (str =&gt; {});
func(str)</code>;

blocks|key|810988|text|用几句话来说:抓住例外。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|810989|我真的很惊讶，至今还没有人回复或评论这篇文章中的例外事件。|810990|细节:下面是一个示例，其中我试图匹配一个以mask_为前缀并以表单字段"name“为后缀的函数。当ReferenceError找不到函数时，它应该在catch部分按您的意愿抛出一个可以处理的JavaScript。|offset|length|style|BOLD|810991|​|810992|function+inputMask(input)+{
++try+{
++++let+maskedInput+=+eval("mask_"%2Binput.name);

++++if(typeof+maskedInput+===+"undefined")
++++++++return+input.value;
++++else
++++++++return+eval("mask_"%2Binput.name)(input);

++}+catch(e)+{
++++if+(e+instanceof+ReferenceError)+{
++++++return+input.value;
++++}
++}
}|code-block|syntax|javascript|810993|810994|entityMap^0|0|0|1D|E|0|0|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|U|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|V|8|@$F|W|G|X|H|I]]|9|@]|A|$]]|$1|J|3|K|5|6|7|Y|8|@]|9|@]|A|$]]|$1|L|3|M|5|N|7|Z|8|@]|9|@]|A|$O|P]]|$1|Q|3|K|5|6|7|10|8|@]|9|@]|A|$]]|$1|R|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|S|$]]

In a few words: catch the exception. 

I am really surprised nobody answered or commented about Exception Catch on this post yet.

Detail: Here goes an example where I try to match a function which is prefixed by mask_ and suffixed by the form field "name". When JavaScript does not find the function, it should throw an ReferenceError which you can handle as you wish on the catch section.

<div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>function inputMask(input) {
 try {
 let maskedInput = eval("mask_"+input.name);

 if(typeof maskedInput === "undefined")
 return input.value;
 else
 return eval("mask_"+input.name)(input);

 } catch(e) {
 if (e instanceof ReferenceError) {
 return input.value;
 }
 }
}</code></pre>
</div>
</div>

blocks|key|810996|text|//+just+pass+your+tested+function+name+instead+of+myFunctionName
if+(+$.isFunction($.fn.myFunctionName)+)+{
++++console.log(+'write+your+code+here.'+);
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|810997|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>// just pass your tested function name instead of myFunctionName
if ( $.isFunction($.fn.myFunctionName) ) {
 console.log( 'write your code here.' );
}
</code></pre>

blocks|key|811012|text|这将验证函数是否存在，如果存在，则将执行。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|811013|me.onChange+&&+me.onChange(str);|code-block|syntax|javascript|811014|这样就可以防止错误TypeError:+me.onChange+is+not+a+function。|offset|length|style|CODE|811015|entityMap^0|0|0|9|14|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

This will verify if the function exists, if so it will be executed

<pre class="lang-js prettyprint-override"><code>me.onChange &amp;&amp; me.onChange(str);
</code></pre>

Thus the error <code>TypeError: me.onChange is not a function</code> is prevent.

blocks|key|2337149|text|现代JavaScript到救援！|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2337150|me.onChange?.(str)|code-block|syntax|javascript|2337151|可选链语法(?.)解决了这个问题。|offset|length|style|CODE|2337152|从JavaScript到ES2020|unordered-list-item|BOLD|2337153|在中输入自版本3.7以来的|2337154|在上面的示例中，如果一个me.onChange属性存在并且是一个函数，则调用它。|2337155|如果不存在me.onChange属性，则什么都不会发生:表达式只返回undefined。|2337156|Note+-如果存在me.onChange属性但不是函数，则会抛出TypeError，就像调用JavaScript中的任何非函数一样。可选的链子并不能使这件事消失。|2337157|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining#Optional_chaining_with_function_calls|1|https://262.ecma-international.org/11.0/#sec-optional-chains|2|https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html^0|0|0|6|2|0|3|0|0|1|A|C|6|1|0|1|C|5|5|2|0|0|14|C|B|0|0|18|5|B|Y|9|0|0|2A|A|B|X|9|0^^$0|@$1|2|3|4|5|6|7|1A|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|1B|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|1C|8|@$I|1D|J|1E|K|L]]|9|@$I|1F|J|1G|1|1H]]|A|$]]|$1|M|3|N|5|O|7|1I|8|@$I|1J|J|1K|K|P]]|9|@$I|1L|J|1M|1|1N]]|A|$]]|$1|Q|3|R|5|O|7|1O|8|@$I|1P|J|1Q|K|P]]|9|@$I|1R|J|1S|1|1T]]|A|$]]|$1|S|3|T|5|6|7|1U|8|@$I|1V|J|1W|K|P]|$I|1X|J|1Y|K|L]]|9|@]|A|$]]|$1|U|3|V|5|6|7|1Z|8|@$I|20|J|21|K|P]|$I|22|J|23|K|L]|$I|24|J|25|K|L]]|9|@]|A|$]]|$1|W|3|X|5|6|7|26|8|@$I|27|J|28|K|P]|$I|29|J|2A|K|L]|$I|2B|J|2C|K|L]]|9|@]|A|$]]|$1|Y|3|-4|5|6|7|2D|8|@]|9|@]|A|$]]]|Z|$10|$5|11|12|13|A|$14|15]]|16|$5|11|12|13|A|$14|17]]|18|$5|11|12|13|A|$14|19]]]]

<h2>Modern JavaScript to the rescue!</h2>
<pre><code>me.onChange?.(str)
</code></pre>
The <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining#Optional_chaining_with_function_calls" rel="noreferrer">Optional Chaining</a> syntax (<code>?.</code>) solves this
<ul>
<li>in JavaScript since <a href="https://262.ecma-international.org/11.0/#sec-optional-chains" rel="noreferrer">ES2020</a></li>
<li>in Typescript since <a href="https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html" rel="noreferrer">version 3.7</a></li>
</ul>
In the example above, if a <code>me.onChange</code> property exists and is a function, it is called.
If no <code>me.onChange</code> property exists, nothing happens: the expression just returns <code>undefined</code>.
Note - if a <code>me.onChange</code> property exists but is not a function, a <code>TypeError</code> will be thrown just like when you call any non-function as a function in JavaScript. Optional Chaining doesn't do any magic to make this go away.

blocks|key|936716|text|我建议使用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|936717|function+hasMethod(subject,+methodName)+{
++return+subject+!=+null+&&+typeof+subject[methodName]+==+"function";
}|code-block|syntax|javascript|936718|第一个检查subject+!=+null过滤掉没有任何属性的空值(null和undefined)。如果没有此检查，subject[methodName]可能引发错误：|offset|length|style|CODE|936719|TypeError：(未定义为null)没有任何属性|blockquote|936720|仅仅检查一个真实值是不够的，因为0和""都是假的，但是确实有属性。|936721|在验证subject不为空之后，您可以安全地访问该属性，并检查它是否与typeof+subject[methodName]+==+"function"匹配。|936722|将此应用于您的代码，您现在可以这样做：|936723|if+(hasMethod(me,+"onChange"))+{
++me.onChange(str);
}|936724|entityMap^0|0|0|5|F|X|4|12|9|1L|J|0|0|G|1|I|2|0|3|7|Z|14|0|0|0^^$0|@$1|2|3|4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|10|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|11|8|@$I|12|J|13|K|L]|$I|14|J|15|K|L]|$I|16|J|17|K|L]|$I|18|J|19|K|L]]|9|@]|A|$]]|$1|M|3|N|5|O|7|1A|8|@]|9|@]|A|$]]|$1|P|3|Q|5|6|7|1B|8|@$I|1C|J|1D|K|L]|$I|1E|J|1F|K|L]]|9|@]|A|$]]|$1|R|3|S|5|6|7|1G|8|@$I|1H|J|1I|K|L]|$I|1J|J|1K|K|L]]|9|@]|A|$]]|$1|T|3|U|5|6|7|1L|8|@]|9|@]|A|$]]|$1|V|3|W|5|D|7|1M|8|@]|9|@]|A|$E|F]]|$1|X|3|-4|5|6|7|1N|8|@]|9|@]|A|$]]]|Y|$]]

I would suggest using:
<pre><code>function hasMethod(subject, methodName) {
 return subject != null &amp;&amp; typeof subject[methodName] == &quot;function&quot;;
}
</code></pre>
The first check <code>subject != null</code> filters out nullish values (<code>null</code> and <code>undefined</code>) which don't have any properties. Without this check <code>subject[methodName]</code> could throw an error:
<blockquote>
TypeError: (undefined|null) has no properties
</blockquote>
Checking for only a truthy value isn't enough, since <code>0</code> and <code>&quot;&quot;</code> are both falsy but do have properties.
After validating that <code>subject</code> is not nullish you can safely access the property and check if it matches <code>typeof subject[methodName] == &quot;function&quot;</code>.
<hr />
Applying this to your code you can now do:
<pre><code>if (hasMethod(me, &quot;onChange&quot;)) {
 me.onChange(str);
}
</code></pre>

blocks|key|811067|text|function+isFunction(+o+)+{+return+null+!==+o+&&+"function"+===+typeof+o+&&+!!o.apply;+}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|811068|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>function isFunction( o ) { return null !== o &amp;&amp; &quot;function&quot; === typeof o &amp;&amp; !!o.apply; }
</code></pre>

blocks|key|937297|text|我更喜欢使用lodash库，如下所示(看起来更干净)：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|937298|if+(_.has(me,+"onChange"))+{
+++//+your+desired+code+here
}

//+or+generic+one+like

if+(_.has(this,+"some+property+or+function+name"))+{
+++//+your+desired+code+here
}|code-block|syntax|javascript|937299|entityMap^0|6|6|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|$]]

I prefer it using <code>lodash</code> library as below (looks much cleaner):
<pre><code>if (_.has(me, &quot;onChange&quot;)) {
 // your desired code here
}

// or generic one like

if (_.has(this, &quot;some property or function name&quot;)) {
 // your desired code here
}
</code></pre>

My code is

<pre><code>function getID( swfID ){
 if(navigator.appName.indexOf("Microsoft") != -1){
 me = window[swfID];
 }else{
 me = document[swfID];
 }
}

function js_to_as( str ){
 me.onChange(str);
}
</code></pre>

However, sometimes my <code>onChange</code> does not load. Firebug errors with

<blockquote>
 me.onChange is not a function
</blockquote>

I want to degrade gracefully because this is not the most important feature in my program. <code>typeof</code> gives the same error.

Any suggestions on how to make sure that it exists and then only execute <code>onChange</code>?

(None of the methods below except try catch one work)

How to check if function exists in JavaScript?

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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我的代码是function getID( swfID ){     if(navigator.appName.indexOf("Microsoft") != -1){          me = window[swfID];     }else{          me = document[swfID];     }...

问如何检查JavaScript中是否存在函数？
EN

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问如何检查JavaScript中是否存在函数？EN