How To Check If Function Exists In Javascript

When you're diving into the world of Javascript, one common task you might face is checking if a particular function exists. Whether you're working on a new project or maintaining existing code, knowing how to check if a function is available can save you time and headaches. In this article, we'll guide you through the process step by step.

There are a few different ways to check if a function exists in Javascript. One approach is to use the `typeof` operator along with the `function` keyword to verify if the function is defined. Here's a simple example:

function myFunction() {
    console.log("Hello, World!");
}

if (typeof myFunction === 'function') {
    console.log("myFunction exists!");
} else {
    console.log("myFunction does not exist!");
}

In this code snippet, we define a function called `myFunction` and then use the `typeof` operator to check if it is a function. If the function exists, we log a message confirming its presence; otherwise, we print a message indicating its absence.

Another common method for checking function existence is using the `hasOwnProperty` method. This approach is especially useful when working with object methods or properties. Here's how you can apply `hasOwnProperty` to verify function existence:

const obj = {
    myMethod: function() {
        console.log("Hello, World!");
    }
};

if (obj.hasOwnProperty('myMethod') && typeof obj.myMethod === 'function') {
    console.log("myMethod exists!");
} else {
    console.log("myMethod does not exist!");
}

In this code snippet, we create an object named `obj` with a method called `myMethod`. By using `hasOwnProperty` along with checking the type of `myMethod`, we can determine if the method exists within the object.

If you're dealing with external libraries or APIs, it's essential to handle situations where functions may not be available due to loading issues or other reasons. One way to handle this scenario gracefully is by utilizing a try-catch block to catch any errors that may occur.

try {
    if (typeof externalFunction === 'function') {
        console.log("externalFunction exists!");
    } else {
        console.log("externalFunction does not exist!");
    }
} catch(error) {
    console.log("An error occurred: " + error);
}

In this example, we attempt to check the existence of an `externalFunction`. If the function exists, we log a message confirming its presence; otherwise, we log a message stating its absence. The try-catch block helps us handle any potential errors that may arise during the execution.

By applying these methods and techniques, you can efficiently check if a function exists in Javascript and handle various scenarios with ease. Whether you're a beginner or an experienced developer, having a solid understanding of function existence checking will undoubtedly be beneficial in your coding journey.