In this post, we will see how to resolve Array.find() is returning undefined and I can’t figure out why Question: In my React project, I have a page that is reading a param called “itemId” and fetching from a list ...

In this post, we will see how to resolve why i get Uncaught TypeError: Cannot set properties of undefined (setting ‘src’)? Question: i tried to modify the src of an img with javascript in php and i got: Uncaught TypeError: ...

In this post, we will see how to resolve Passing Undefined to Optional Field Question: I have the following approach for dealing with passing down potentially undefined objects into optional properties: Seems a bit clunky- using an if statement and ...

In this post, we will see how to resolve JavaScript this is undefined when function called in a loop Question: I have the following code with the behavior explained in the comments. What could be the reason why "this" is ...

In this post, we will see how to resolve Getting TypeError: undefined is not a function – Each time I Ctrl + Save, it goes, and next time Ctrl + S it comes back Question: Getting this error – TypeError: ...

Question: How do I check a variable if it’s null or undefined and what is the difference between the null and undefined? What is the difference between == and === (it’s hard to search Google for “===” )? Best Answer: ...

Question: We are frequently using the following code pattern in our JavaScript code Is there a less verbose way of checking that has the same effect? According to some forums and literature saying simply the following should have the same ...

Question: I have a global variable in JavaScript (actually a window property, but I don’t think it matters) which was already populated by a previous script, but I don’t want another script that will run later to see its value ...

Question: I wanted to check whether the variable is defined or not. For example, the following throws a not-defined error How can I catch this error? Best Answer: In JavaScript, null is an object. There’s another value for things that ...

Question: I want to know what the difference is between null and undefined in JavaScript. Best Answer: undefined means a variable has been declared but has not yet been assigned a value : null is an assignment value. It can ...