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One of the most common errors in Chrome DevTools is “cannot read property of undefined.” Here are some of the causes and fixes!

While developing an application with Angular, you may encounter a few errors. These errors do not occur very frequently but can be quite confusing and annoying (especially if the problem is something obvious that you missed). These errors can be related to syntax, errors in data or API issues.

This troubleshooting guide for Google Chrome developers will talk about one of the most common errors you may encounter in DevTools—“cannot read property of undefined.” There can be many reasons why you get the “cannot read property of undefined” error. In this article, we will explore some ways to troubleshoot and solve them as quickly as possible.

What Does ‘Cannot Read Property of Undefined’ Mean?

In programming, you will come across many kinds of errors. One common error you may come across while using Google Chrome Developer Tools while debugging your application is “cannot read property of undefined.”

This error is thrown when the code has a syntax error that breaks the execution of the program and prevents the execution of any other statement. The “cannot read property of undefined” error essentially means that the browser could not understand the expression used.

This can happen for many reasons. One of the reasons for this is that the code is not being executed due to a syntax error in the code. This error can occur if you are trying to access a variable or a property that has not been declared yet. This is a common error that happens when you are trying to access a variable or a property that has not been declared yet.

Why Does It Happen?

The “cannot read property of undefined” error can occur when you are trying to access a variable or a property that has not been declared yet. This error can also happen if you try to access an implicit template that has not been loaded yet.

How Can You Fix It?

Make Sure the Rendering Variable Is Defined

There are a few ways you can fix the “cannot read property of undefined” error. If you are trying to access a variable or a property that has not been declared yet, you might have to declare it first.

For example, this is a flawed function:

function myFunc(a) {
console.log(a.b);
}

var myVar;
myFunc(myVar);

And running this script gives the error:

TypeError: Cannot read properties of undefined (reading 'b')

Now, to fix this error we can simply assign the variable causing the error to a value, like so:

function myFunc(a) {
    console.log(a.b);
}

var myVar = {
    b: 'myProperty'
};

myFunc(myVar);

And now if we run it would print out the results:

myProperty

Determine Whether a Template Is Loaded or Not

If you are getting the “cannot read property of undefined” error while using Angular’s View Children and View Children on a directive, you should check if your template is loaded or not. You can do this by adding a breakpoint in the debugger.

For example, we can write this to use the safe navigation operator if foo and bar are objects.

{{ foo?.bar?.name }}

And if we want to check for arrays, we can use *ngIf like this:

<div *ngIf="arr && arr.length > 0">
  {{ arr[0].name }}
</div>

Here use > 0 to make sure the length of arr && arr.length is more than nothing (0) which in turn confirms that it is present.

Check Whether There Is a Wrapper-Rendering Conflict

If the “cannot read property of undefined” error is related to a wrapper-rendering conflict, it can be confirmed when you see a yellow warning in the Console tab. If you are seeing this warning in your Console tab and you don’t know what it means, you should check how the modules are being loaded. This problem can be solved by injecting the providers for the modules that are causing the wrapper-rendering conflict.

Confirm Whether You Have Used the Correct Syntax While Accessing a Variable or Property

If you are accessing a variable or a property that has been declared, yet the browser is giving the “cannot read property of undefined” error, you should confirm whether you have used the correct syntax. You have to be careful while using curly braces and colons while accessing variables or properties.

You can also add some checks in your components itself too to avoid such errors like:

getContent(): string {
    const dataToReturn = this.pageContent && this.pageContent.content && this.pageContent.content.rendered.replace(/\[(.+?)\]/g, "");
    return dataToReturn
  }

How Can You Prevent This Error?

Preventing the “cannot read property of undefined” error can be quite tricky as it is hard to know when and where it will happen. However, there are a few things you can do to prevent it from happening.

First, make sure you are not missing any curly braces or semicolons. This is especially important if you are writing in a language like JavaScript, where those are optional. You should also make sure that you are not referencing a variable or a function that has not been declared yet. This can be quite tricky as you might not even notice that you are referencing an undefined variable or function.

Finally, make sure you are not referencing a variable or a function whose name has a different casing than what is in your source code. This can easily happen if you are typing the code quickly and not paying attention to the casing.

Final Words

The “cannot read property of undefined” error can be quite confusing and annoying. It can happen if the code has a syntax error that breaks the execution of the program and prevents the execution of any other statement. Errors like this are a part of the development process, and even the most experienced web developers come across them in their day-to-day work. Web developers should be aware of the most common errors and learn how to solve them. Understanding how to solve these errors will make your web application development process much easier and smoother.

We hope this article helped you understand more about the “cannot read property of undefined” error that can be encountered while using Angular.


About the Author

Vyom Srivastava

Vyom Srivastava is an enthusiastic full-time coder and also writes at GeekyHumans. With more than four years of experience, he has worked on many technologies like Apache Jmeter, Google Puppeteer, Selenium, etc. He also has experience in web development and has created a bunch of websites as a freelancer.

 

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