jQuery Check if Function Exists Example

jQuery code snippet to check whether a function exists within the JavaScript code. This can be easily achieved by using the jQuery.isFunction() function. Useful for checking if a jQuery function exists before calling it!



    function somenoobfunction() {
    }  
<p>    // using jQuery
    if ($.isFunction(window.somenoobfunction)) {
		//execute it
        somenoobfunction();
    } else {
		//doesnt exists... cry?!?
        document.writeln('somenoobfunction does not exist');
	}

Note: As of jQuery 1.3, functions provided by the browser like alert() and DOM element methods like getAttribute() are not guaranteed to be detected as functions in browsers such as Internet Explorer.

Further reading: http://api.jquery.com/jQuery.isFunction/

Frequently Asked Questions (FAQs) about jQuery Check Function

How can I check if a function exists in jQuery before calling it?

In jQuery, you can check if a function exists before calling it by using the ‘typeof’ operator. This operator returns a string indicating the type of the unevaluated operand. If the operand is a function, ‘typeof’ returns “function”. Here’s an example:

if (typeof functionName == 'function') {
functionName();
}
In this code, ‘functionName’ is the name of the function you want to check. If the function exists, it will be called; if not, nothing will happen.

What happens if I call a function in jQuery that doesn’t exist?

If you try to call a function that doesn’t exist in jQuery, you will get a JavaScript error saying that the function is not defined. This can cause your script to stop executing, which can lead to unexpected behavior in your web application. That’s why it’s important to always check if a function exists before calling it.

Can I use the ‘typeof’ operator to check if a function exists in plain JavaScript?

Yes, you can use the ‘typeof’ operator to check if a function exists in plain JavaScript, not just in jQuery. The ‘typeof’ operator is a part of the JavaScript language and works the same way in jQuery as it does in JavaScript.

How can I check if a jQuery plugin is loaded before using it?

You can check if a jQuery plugin is loaded by using the ‘typeof’ operator and checking if the plugin’s main function is defined. Here’s an example:

if (typeof $.fn.pluginName == 'function') {
// Plugin is loaded
}
In this code, ‘pluginName’ is the name of the plugin you want to check. If the plugin is loaded, the code inside the if statement will be executed.

Can I check if a function exists in a specific jQuery version?

Yes, you can check if a function exists in a specific jQuery version. However, this requires knowledge of which functions were added or removed in each version of jQuery. You can find this information in the jQuery documentation or by searching online.

What is the performance impact of checking if a function exists before calling it?

The performance impact of checking if a function exists before calling it is minimal. The ‘typeof’ operator is very fast and will not noticeably slow down your code, even if you use it frequently.

Can I check if a function exists in a jQuery object?

Yes, you can check if a function exists in a jQuery object. You can do this by using the ‘typeof’ operator and checking if the function is defined on the object. Here’s an example:

var obj = $('#myElement');
if (typeof obj.functionName == 'function') {
obj.functionName();
}
In this code, ‘functionName’ is the name of the function you want to check. If the function exists on the object, it will be called.

Can I check if a function exists in a jQuery plugin?

Yes, you can check if a function exists in a jQuery plugin. You can do this by using the ‘typeof’ operator and checking if the function is defined on the plugin’s main function. Here’s an example:

if (typeof $.fn.pluginName.functionName == 'function') {
$.fn.pluginName.functionName();
}
In this code, ‘pluginName’ is the name of the plugin and ‘functionName’ is the name of the function you want to check. If the function exists in the plugin, it will be called.

Can I use the ‘in’ operator to check if a function exists in jQuery?

Yes, you can use the ‘in’ operator to check if a function exists in jQuery. The ‘in’ operator returns true if the specified property is in the specified object. Here’s an example:

if ('functionName' in $) {
$.functionName();
}
In this code, ‘functionName’ is the name of the function you want to check. If the function exists, it will be called.

Can I check if a function exists in a jQuery object or plugin without calling it?

Yes, you can check if a function exists in a jQuery object or plugin without calling it. You can do this by using the ‘typeof’ operator and checking if the function is defined, without actually calling the function. Here’s an example:

if (typeof $.fn.pluginName.functionName == 'function') {
// Function exists
}
In this code, ‘pluginName’ is the name of the plugin and ‘functionName’ is the name of the function you want to check. If the function exists, the code inside the if statement will be executed, but the function will not be called.