In this article, you'll take a closer look at the meaning of the error "Cannot read property split of undefined", what causes it, some examples, and techniques to prevent it.
As a developer, you're constantly dealing with user inputs as strings. Understanding this error will enable you to work with strings more effectively and will help prevent your users from having a bad experience with your application.
The split() method divides a string into an array of substrings based on the separator argument passed in. Let's look at a few code examples below:
Call the split() method on the string:
After running this code in your console, you'll see the split() method in action:
The split() method can be a very useful tool in algorithms involving string data types. For example, you could use it when you need to reverse a string, or remove spaces from within a string.
The error "Cannot read property split of undefined" can occur when performing any of these types of operations if the variable is undefined. Furthermore, when you are working on a project, there are several other scenarios where this error can occur, including the following:
Let's look at a concrete example. Suppose you'd like to return a message depending on the value of n. The variable, message, is initialized on the first line. When n is greater than five, the message is ‘This number is greater than five’, and the Split() method is called on the message.
The output will be:
The value of the message when n is less than five is not defined. As such, when n is less than five, the split function will be called on the undefined message, which will return an error. For example, calling greaterThanFive(4) will throw an error, as can be seen in the screenshot:
Now that you understand why this error occurs and its potential impact on your work, how can you avoid it? There are several ways of doing this.
Check the data type of your variable before proceeding to call the split() method. If the data type is a string, then you can proceed with your splitting operation. You can check a data type using the typeof() method, then call the split() method using conditional statements like if and else, as shown in the following code:
The first line in the code snippet defines the sample variable you want to check with the conditional statement in the next line. If the conditional if statement is true, then the sample variable is split; if it returns false, then the algorithm returns the original variable. This is a simple, easily added check to catch and address the Cannot read property split of undefined error.
When using TypeScript, you're able to annotate your code with types the way you would in other strongly typed languages. This enables deeper levels of IntelliSense and in-editor errors and hints. In this case, assuming you're using a code editor with TypeScript support, the second call to splitString will show you an error directly in your code editor when you try to invoke the function with an invalid type. This can save a lot of time and effort, as it drastically shortens the feedback loop when it comes to type-related errors, allowing you to find and fix them before your code ever runs.
If the variable the split() method is called on resolves to undefined, you can assign an alternative value to it.
Here, the sample variable is declared at undefined in line one. Rather than calling the split method directly on the variable, line two assigns an alternative value so the split operation will execute without error.
Optional chaining allows you to optionally call the split() method, depending on if a variable is defined or not. If the variable is defined, the function runs as expected; if it's undefined or null, it stops and returns ``undefined`. This is especially useful in situations where the variable is optional, and may or may not be present.
Because the property location is not present in the person object, the code returns undefined.
Wrapping your code in a try and catch block. While this method doesn't prevent the error from occurring, it does ensure that if it occurs, it's handled gracefully. This method is especially useful when there are edge cases that cannot be accounted for in your algorithm. You can read more about try-catch in this blog post here.
One of the benefits of the try and catch block is that it allows developers to handle errors seamlessly, and to customize your error messages. Putting your function in a try and catch block would ensure that a simple, easy-to-understand response is returned to the client if an error occurs.
In this post, you have seen the many different scenarios that can result in a "Cannot read property split of undefined" error showing up in your application. You've also learned that carrying out data type checks, assigning alternative values to variables, and exception handling with a try and catch block are some of the best ways to handle the error in your project.
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